Physics Gce o Level Syllabus 2010 2
NOT YET DONE! ONLY REVISED EDITION!...
PHYSICS GCE O LEVEL SYLLABUS 2010 THEME 1: GENERAL PHYSICS Name: ________________________________ Class:__________ CHAPTER 1: PHYSICAL QUANTITIES, UNITS AND MEASUREMENT 1.1 UNITS AND SYMBOLS Unit Prefixes Prefix/Abbreviation Power Prefix/Abbreviation Power nano/n 10-9 deci/d 10-1 -6 10 kilo/k 103 micro/ -3 6 milli/m 10 mega/M 10 -2 9 centi/c 10 giga/G 10 1.2 SCALARS AND VECTORS Scalars are quantities that have magnitude only. Vectors are quantities that have both magnitude and direction. SCALAR QUANTITIES VECTOR QUANTITIES mass weight distance displacement speed velocity time acceleration pressure force energy moment volume density SI Units We use 0.1 precision when we write or round off to 3 significant figures Measurement of Small unit (e.g. 0.xx) Large units (>2) Time Seconds/s Length Millimetre/mm; Centimetre/cm Metre/m Mass Grams/g Kilogram/kg Current Milliampere/mA Ampere/A Power Watts/W Kilowatts/kW; Megawatts/MW Force Newton/N Newton/N Pressure Pascal/Pa with standard form Pascal/Pa Energy Joules/J Kilojoules/kJ; Megajoules/MJ
Resultant Force/Net Force Vectors 1. Parallel and same direction vectors E.g. A person pushes a box with a force of 50N. At the same time, a force of 60N is pulling the box to the direction the man is pushing. What is the magnitude of the net force and state the direction of the net force. Magnitude = 50N + 60N = 110N Direction = To the right 110 N, right 2. Parallel but opposite vectors E.g. Two opposite forces to the right and left, 40N and 60N respectively, are pulling a box. State the magnitude and direction of the resultant force.
The direction of resultant force is the direction of the force which is the greatest which, in this case, is left. The magnitude of the resultant force is the difference between the larger force and smaller force, 60N – 40N = 20N. 3. Two forces of different directions and magnitude E.g. A kite of weight 4.0N was flown from point X to Y. There was an upward force of 6.0 N by the wind perpendicular to the line XY. Draw a scale vector diagram. You should state the magnitude of the resultant force and the direction (angle between horizontal to the net force).
Step 1: Draw a parallelogram, scaled, with same length as the forces.
Step 2: Draw a diagonal across the parallelogram, connecting the point between the force 6.0N and 4.0N. This is the resultant force, FR (the upward force pulling kite up and also the direction of the force)
Step 3: Measure the length of the diagonal. Then with your measurement, compare with the scale. This is the magnitude of the resultant force. Then to find the direction, draw a horizontal line, parallel to the ground, and measure with a protractor between horizontal to net force. Scale = 1cm:1N
Step 1: Draw the scaled lines of forces, with each starting points MUST start from the END point of EACH previous line of force. Then draw the resultant force from the VERY START of the force (from barge) to the VERY END of the force. Determine the magnitude and direction (from horizontal to net force), which in this case is 1o but we round it off as right. The direction MUST follow the direction of the GREATEST FORCE. *NOT TO SCALE. THE SCALE IS FOR YOUR REFERENCE ONLY. WHEN YOU DRAW, USE REAL SCALE!*
1.3 MEASUREMENT TECHNIQUES Length Metre Rule Metre rule is used to measure length of 0 – 1m with 0.1cm precision To read the length of the object: Look vertically above the metre rule to avoid parallax error (error in reading due to incorrect position of the eye),
*NOT TO SCALE. THE SCALE IS FOR YOUR REFERENCE ONLY. WHEN YOU DRAW, USE REAL SCALE!* 4. More than 2 forces of different directions and magnitude E.g. A barge is pulled by 3 forces. Determine the magnitude and direction of the resultant force (direction where the barge would move) Vernier Calipers Vernier calipers used to measure small length of 0 – 15cm with 0.01cm precision
The main scale is up to 0.1 cm precision. It’s in cm. The vernier scale is up to 0.01 cm precision. It’s in cm too. Add the reading of vernier scale with main scale. To read a vernier calliper: STEP 1: Look where the zero mark of the vernier scale coincide with the main scale. This is your centimeter length on the main scale, correct to 0.1cm. In this case, it’s 3.1 cm.
STEP 2: Look where the marking on vernier scale coincide with the marking on the main scale. This is your centimetre length too, but correct to 0.01 cm. In this case, the 4th marking on vernier scale coincides with the marking on the main scale. Hence, the reading of vernier scale is 0.04 cm.
STEP 3: Add the reading from vernier scale with the reading on the main scale. READING = (3.1 + 0.04) cm = 3.14 cm
Micrometer Screw Gauge Micrometer gauge used to measure small length of 0-2.5cm with 0.01mm precision (e.g. for wire diameter, paper thickness, etc that is very fine)
The main scale on the sleeve is up to 0.1 mm precision. It’s in mm. The circular scale on thimble is up to 0.01 mm precision. It’s in mm too. Add both readings to get the length in mm. To read a micrometer gauge: STEP 1: After placing the object between anvil and spindle, look where the mark of the main scale coincide with the circular scale. This is your millimeter length on the main scale, correct to 0.1mm. In this case, it’s 4.5 mm.
Preventing zero error: When the jaws of vernier touch each other, the zero markings on both vernier scale and main scale should coincide each other. However, if they don’t coincide, we have to deduct our reading, with object inserted, with the zero error. STEP 2: Look where the marking on the circular scale coincides with the horizontal line on the main scale. This is your millimetre length on the circular scale, correct to 0.01mm. The 12th division coincides with the length and therefore, the thimble reads 0.12mm.
STEP 3: Add both readings. This is length of the object in mm, correct to 0.01mm READING = (4.5 + 0.12) mm =4.62 mm
Preventing zero error When the anvil touch each other but the zero marking on the circular scale do not coincide with the main scale and the main scale doesn’t coincide at 0.0mm, then we have to deduct our reading, with our object inserted, with the zero error.
Ticker Tape Timer A ticker tape timer is an electrical vibrator which oscillates by marking a dot on a paper 50 times a second. The faster the paper moves, the further apart the dots. If there are 10 dots marked on paper, then time taken to mark 10 dots is 10 x 0.02 s = 0.2 s. Between each dot, it represents 1 50 oscillations = 0.02 seconds.
Time Time is measured in seconds. A motion which is repeated is oscillation (e.g. a pendulum from rest swings to displaced position then back to its rest position is one oscillation). The time in which one oscillation occur is period. Watch Watches are used to measure long time intervals (e.g. every 1 minute for 10 minutes). Usually, we use minutes. Stopwatch Stopwatches are used to measure short term intervals. Digital stopwatches has 0.01 s precision while analogue stopwatches has 0.1 s precision. The reaction time affects the reading of the stopwatch, that is the time when you press the start and stop button of the stopwatch, might be late for a few hundredths of a second.
END OF CHAPTER 1
PHYSICS GCE O LEVEL SYLLABUS 2010 THEME 2: NEWTONIAN MECHANICS Name: ________________________________ Class:__________ CHAPTER 2: KINEMATICS 2.1 SPEED, VELOCITY AND ACCELERATION Distance and Displacement Distance is the total length of travel, irrespective of direction of motion Displacement is the distance moved in a particular direction E.g. 1. A person walks from A to B and returns to A. The distance AB is 1.5km. State the distance walked and the displacement of the boy from A 1.5km A B Distance = 2 (1.5 km) Displacement = 0 km (because he didn’t = 3.0 km move from original position) E.g. 2. A student walks from A to B, then B to C and finally from C to D. The diagram below shows the plan of the path of the student. What is the distance travelled by the student and state his displacement from A to D. 2km D C 0.5km
Displacement A B 2 km Distance = (2 + 2 + 0.5) km Displacement = 0.5 km, North = 4.5 km Speed Speed is the distance moved by an object per unit time (rate of change of distance) s= where: s = speed; d = distance moved; t = time taken This gives you the CONSTANT SPEED, with unit in m/s or km/h whereas for NON-UNIFORM SPEEDS, to find the AVERAGE SPEED, we use s=
Velocity Velocity is the distance travelled per unit time in a particular direction (rate of change of displacement). The unit is m/s or km/h. v= where: v = velocity; d = displacement; t = time taken E.g. What is the velocity of the student walking from A to D with the path below if he reaches D in 2h and that his velocity is constant? Find the average speed.
= 0.25 km/h from A = 2.25 km/h Acceleration Acceleration is the rate of change of velocity. The unit is m/s2 a= where: a = acceleration; v = final velocity; u = initial velocity; t = time taken E.g. A car moves from rest and reaches point B with velocity of 25 m/s in 10 seconds. State its acceleration from rest. a= 2
= 2.5 m/s The driver now at B sees a child crossing across the road. He starts to apply the brakes. The car retards/decelerates (indicated by negative acceleration) until it comes to rest 5 seconds later. State the deceleration. a= = -5.0 m/s2 2 2 We can write as deceleration = 5.0 m/s OR acceleration = – 5.0 m/s
Copyrights AF/PS/2009/2010 2.2 GRAPHICAL ANALYSIS OF MOTION Distance-time Graph The gradient of distance-time graph gives the speed
6 Speed-time Graph The gradient of speed-time graph gives the acceleration The area under the graph of speed-time graph gives the distance moved.
Copyrights AF/PS/2009/2010 Solving a Speed-Time Graph The graph represents the motion of a car along a straight road. Determine:
7 (v) The total distance travelled by the car from t = 0s up to t = 35s. d = 192m + (5.5 x 28) m + ( x (28+12) x 7.5) m + ( x (28+12) x 6) m + 28 m = 192m + 154m + 150m + 120m + 28m = 644m (vi) The way the car comes to rest at t = 40s. The car comes to rest with a non-uniform increasing deceleration (gradient) CHAPTER 3: DYNAMICS
(i) The deceleration of the car when it enters the town. The deceleration of a speed-time graph = gradient a = = a = – 3.47 m s-2 deceleration = 3.47 m s-2 (ii) The acceleration of the car as it exits the town. a= = a = 4.33 m s-2 (iii) The time taken for the car being inside the town with a constant speed. t = (28 – 12) s = 16 s (iv) The distance between the entrance and exit of the town. Distance = area under the graph d = 16 s x 12 m s-1 = 192 m
CHAPTER 4: MASS, WEIGHT AND DENSITY CHAPTER 5: TURNING EFFECTS OF FORCES CHAPTER 6: DEFORMATION CHAPTER 7: PRESSURE
CHAPTER 8: ENERGY SOURCES AND TRANSFER OF ENERGY 8.1 FORMS OF ENERGY Energy – the capacity to do work Unit: Joules (J) STOP LIGHT! When a system does work, the energy content decrease, while the system on which work has been done increase in energy content. Example: ball dropped from a high place will lose Ep and gain Ek. Kinetic Energy (Ek) Is the energy a body possesses due to its motion. Formula: Ek = mv
Non-Renewable energy - Will run out soon and takes many years to form Renewable energy - Can be made and renewed. It’s a clean source of energy Problems with the energy we use everyday - Burning of fossil fuels produces fumes which contributes to air pollution - Waste gases of burnt fuel such as sulphur dioxide contributes to greenhouse effect and acid rain. - Non-renewable energy cannot be replaced
Where m = mass, v = velocity Potential Energy (Ep) Is the energy stored in object due to its position, state or shape. Types of Potential Energy: Elastic potential energy: - Possessed when an object is compressed / stretched Gravitational potential energy: - Energy a body possesses due of its position relative to the ground Chemical potential energy: - In substances that can be burnt Gravitational Potential Energy = mgh m = mass, g = gravitational field strength, h = height Thermal Energy The total kinetic energy of atoms / molecules in the body Occur when temperature > 0 Kelvin Thermal energy of a body = Absolute temperature of body The Energy We Use Everyday Renewable Energy is energy resource that can be replaced Non-renewable Energy is energy resource that cannot be replaced
Solutions: - Use renewable energy sources as they don’t contribute pollution 8.2 ENERGY CONVERSION AND CONSERVATION Energy Conversion The change of one form of energy into another form of energy e.g: a boy kicks a ball: Chemical potential energy Kinetic energy Energy Conservation Principle of conservation of energy: Energy can’t be created/destroyed; change from 1 form to another. The total mechanical energy stays the same E,g. In power stations, energy from coal... 8.3 WORK W= Force x Distance moved No acceleration/movement = no work Unit – Joule (J) 8.4 POWER Power is rate of doing work P=
SI Unit – WATTS (W), 1 W = 1 J/s 1 hp (horsepower) = 750W
PHYSICS GCE O LEVEL SYLLABUS 2010 THEME 3: THERMAL PHYSICS Name: ________________________________ Class:__________
CHAPTER 9: TRANSFER OF THERMAL ENERGY 9.1 STATES OF MATTER 3 states - solid, liquid and gases
An elevator with load weighing 1600kg takes minutes to elevate from ground floor to 4th floor. Given the height of a floor is 4m and the elevator has same height as each floor, what’s the power of elevator’s motor to do the work? Take gravity = 10 N/kg ∴ F = mg
= 1600 kg x 10 N/kg
= 16 000 N = 5 688.89 W Work done = F x d = 5.69 kW (3 s.f.) = 16 000 N x (4 x 4m) = 256 000 J Example: A pulley pulls a trolley consisting goods weighing 40 kg in total, up a ramp as shown in the illustration below in 12 seconds. Calculate the power of the motor.
Table 8.1: Different properties of matter
Diagram 8.1: Different states of matter
F = mg
= 40 kg x 10 N/kg
= 400 N
= 333.3 W = 333 W (3 s.f.)
Work done = F x d (vertical distance) = 400 N x 10 m = 4 000 J
8.2 BROWNIAN MOTION - Observed first in 1827 by Robert Brown when he saw pollen grains moving randomly when suspended on water. - To prove the existence of particles of matter moving randomly. Smoke particles move continuously and haphazardly when floating in air in random directions as the particles are bombarded by unseen, fast-moving air particles. Temperature increase vigorous movement of smoke particles Smaller smoke particles vigorous movement of smoke particles
8.3 KINETIC MODEL Kinetic theory of matter – All matter is made up of large number of atoms/molecules in continuous motion. Motion of Molecules and Temperature Higher temperature vigorous movement of particles Surrounding air molecules move faster and hit surrounding particles with greater force because thermal energy is transferred to the molecules and gain more kinetic energy. Motion of Molecules and Pressure When gas particles hit walls of container, they exert pressure on wall. ∵P = , force acting on container rises gas pressure Temperature Increases Pressure Increases When temperature of gas in container increases, molecules move faster and hit walls more frequently and violently, rising the pressure. Temperature Increases Volume Increases When temperature of gas in container increases, molecules move faster. To maintain same pressure (less frequent hitting of walls), volume increased. Volume Decreases Pressure Increases When a container volume is halved, the number of molecules per unit volume is doubled, so the hitting frequency to the wall is doubled more pressure. CHAPTER 8 ENDS HERE
CHAPTER 9: TRANSFER OF THERMAL ENERGY 9.1 CONDUCTION Conduction – the process whereby thermal energy is transmitted through a medium from one place to another. How Conduction Works When one rod end is heated molecules there gain energy and vibrate faster and would collide with their next less energetic neighbours. With this, some energy is transferred to the neighbouring molecules to gain kinetic energy, thus thermal energy is passed on by vibrating molecules and this continues until the cold end reaches same temperature as the hot end. THERE IS NO NET MOVEMENT OF MOLECULES! Why Solid Conducts Better Than Liquids or Gases? Solid molecules are closer together so kinetic energy is transferred quickly Why metals act as better conductors? This is because metals have free electrons. When heated, free electrons gain energy and move faster. They can travel between spaces within molecules before colliding with other electrons & molecules, thus transferring energy to them more. Poor Conductors - INSULATORS 9.2 CONVECTION Convection – the process whereby thermal energy is transmitted from one place to another by movement of heated particles of gas or liquid.
PHYSICS GCE O LEVEL SYLLABUS 2010 THEME 4: WAVES Name: ________________________________ Class:__________
12.3 WAVE TERMS Wavefront – the line joining all crests of a wave / all identical points on a wave. The direction of wave travel is always perpendicular to wavefront
CHAPTER 12: GENERAL WAVE PROPERTIES 12.1 DESCRIBING WAVE MOTION Wave is the transfer of energy through vibrations Water Waves The Ripple Tank Circular wavefront
Horizontal dipper is dipped up and down by motor, generating continuous waves. Light iluminates white screen through the ripples, casting image of ripples on it. Ripples represented by dark and bright fringes; Dark – troughs, Bright – crests 12.2 TRANSVERSE AND LONGITUDINAL WAVES Transverse Waves Waves which travel in perpendicular direction to the direction of the vibrations
CREST is the highest point of a wave; TROUGH is the lowest point of a wave AMPLITUDE is the maximum displacement (height) measured from the rest position (indicated with straight line) WAVELENGTH () is the distance between 2 crests/troughs. The distance any of the two identical points is the same throughout the wave
Longitudinal Waves Waves which travel in parallel direction to the direction of the vibrations
High Frequencied Wave
Low Frequencied Wave
FREQUENCY (f) is number of crests/troughs that pass a point per second. Unit: Hz PERIOD (T) is the time taken to generate one complete wave (or wavelength)
Formula: T =
SPEED (v) is the distance moved by a wave in one second
Formula: v = or v = f
12.4 GRAPHICAL REPRESENTATION OF WAVES Displacement-Position Graph You’ll be able to find out the: (i) wavelength, (ii) amplitude
Displacement-Time Graph You’ll be able to find out the: (i) amplitude, (b) period, (c) frequency
CHAPTER 13: LIGHT 13.1 REFLECTION OF LIGHT Light rays from object make us see the object when the rays enter our eyes Luminous objects – give off light by their own Non-luminous objects – does not give off light; reflects light from a light source The Laws of Reflection Incident ray, Normal and Reflected ray lie on the same plane Angle of incidence is equal to Angle of Reflection Angle of incidence – angle between incident ray and normal Angle of reflection – angle between reflected ray and normal
Tsunami is a series of waves with extremely long wavelength and period generated in a lake or sea by impulsive disturbance When crosses deep ocean, wavelength may be hundred km or more but the amplitude is 1 km or less – cannot be felt or seen. Speed = 1000km/h When reacehes shallow waters, velocity diminishes and the amplitude increases, therefore creating devastation WAVE REFLECTION
Diffuse and Regular Reflection Rough Surfaces (e.g. table) When light rays strike different parts of tiny protrusions on the surface, rays are reflected in many directions – diffuse reflection. Each ray obeys the law of i = r. Smooth Surfaces (e.g. mirror) There are no up-and-down surfaces so all the rays reflect in the same manner – regular reflection. The Image in a Plane Mirror Virtual (cannot be formed on screen / light rays cannot pass through it like mirror) Upright (Erect) Same size as object Laterally inverted (left-to-right inversion) Distance between object and mirror = Distance between image and mirror
END OF CHAPTER 12
Ambulance is written backwards so that drivers can see by rear-view mirror
Ray Diagrams and Mirror To draw an object reflected to the mirror to be seen to the eye:
Light waves from air into glass block slows down. Glass is optically denser than air as it slows down the speed of light When light travels from a lighter medium to a denser medium, refracted ray bends towards the normal. When light travels from a denser medium to a lighter medium, refracted ray bends away from the normal. When light travels enters another medium of different densitiy at perpendicular from the normal, there is no ray deviation (no refraction). PRACTICAL ACTIVITY: Investigating refraction of light into glass block
STEP 1 Draw a line from Object (O) to Mirror (M) then continue from Mirror (M) to Image (I). Make sure the lines are perpendicular to M and OM = MI. STEP 2 Draw lines from the image to the eye to represent reflected rays. Behind the mirrror should be in dotted lines while when reaching out the mirror use solid lines. STEP 3 Draw lines from the object connecting to reflected rays in front of the mirror Using Reflection Periscope Two plane mirrors are placed at 45o to stem of periscope Incident rays from object enter the periscope The ray strikes the first mirror and the image is laterally inverted. The inverted ray strikes the second mirror which re-inverts the ray to normal and reach the eye
Place glass block on paper and draw the outline of it. Shine a ray source from an angle, then draw points on the incident ray and emergent ray. Connect the points on incident ray, and then connect another points on emergent ray. At point of incidence and point of emergence, draw perpendicular line to the glass block outline to represent the normal line. Inside the outline join the point of incidence and point of emergence with a straight line, and then measure the angle of incidence, refraction and emergence. Laws of Refraction 1. Incident ray, refracted ray and normal at point of incidence lie on the same plane. 2. For the two media,
ratio is constant, where i is angle of incidence while r is
angle of refraction (Snell’s Law) Constant ratio is known as refractive index (n), where the formula is n =
Mirror in Meter A mirror is placed directly under the pointer so that the eye will look at the correct position disregarding parallax error 13.2 REFRACTION OF LIGHT The bending of light when it passes from one medium to another – refraction
. The greater n, the more refraction towards normal
Example: A ray of light travels from a liquid of refractive index 1.33, into the air. The angle of incidence is 30o. State the degree of the angle of refraction. Note: since ray travels in same manner when shone from air, the formula is n =
Copyrights AF/PS/2009/2010 anl
(a = air, l = liquid; means equation when light ray is FROM air TO liquid)
1.33 = o
sin r = 1.33 x sin 30 = 0.665 r = 41.7o Refractive Index and Speed of Light refractive index (n) = Example: Light ray in the air when enters diamond of refractive index 2.42 retards from its 8 -1 original speed 3.0 x 10 m s . State the speed of light in diamond. n=
(a) Light ray enters the block at normal (angle of incidence = 0), there’s no deviation (b) Angle of incidence increases, hence angle of refraction increases too (c) Refracted ray now passes exactly along air-glass boundary – the angle of incidence is the critical angle
2.42 = (d) Angle of incidence > critical angle – ray doesn’t leave glass; reflected internally
v= = 1.24 x 108 m s-1 From above: Higher medium optical density slower light speed
Critical Angle and Refractive Index From the formula of refractive index, to find critical angle: n=
Floating Brick? The brick appears floating as light from the brick is refracted at water-air boundary and bent away from normal. Our eye receives light in a straight line, therefore we see the brick higher than the actual point. The formula for refractive index of this phenomenon is n =
(refer example law of refraction)
= = sin critical = Example: Find the critical angle for a glass block of refractive index 1.50 sin critical = critical = sin-1 (
= 48.7 Applications of Total Internal Reflection Total Internal Reflection Criterias for occurance of total internal reflection: Light travels from an optically denser medium to optically less dense medium Angle of incidence is greater than critical angle (angle of incidence in denser medium when the angle of refraction in the other medium = 90o)
Binoculars and Periscope Light enters the lens and gets inverted (for binoculars) When the (inverted) light strike the series of prisms at an angle greater than 42o (critical angle), it gets reflected internally and turned around; the image become upright and then the light emerges out of prism and enters observer’s eyes. This reduces the length of instrument and produces erect image of the object. Single Lens Reflex (SLR) Camera - When light enters lens, it gets inverted and the mirror reflects it onto pentaprism in the SLR camera as laterally inverted light. - In pentaprism, light ray turned around inside the camera, thus the image is erect.
Fibre Optics (Diagram 13.1) Transmit data from one place to another, used in telecommunication & endoscope When light ray or pulses of laser enters the fibre, it’s internally reflected from the sides. These signals are usually sent in bundles of optical fibre. Advantages are: They are thinner and lighter They are made of glass which is cheaper than copper cable transmission lines They high quality information transmission over very long distances with no significant signal loss They carry greater volume of telephone calls, computer data & TV pictures 13.3 THIN LENSES Lens are used in spectacles, cameras, telescopes, microscopes, human eyes, etc. Converging Lenses are thicker in the middle than at the edges They bring light ray passing through it together Diverging Lenses are thinner in the middle and broader at the edges They spread out light ray passing through it
Optical Centre (C) is the point in the middle of lens surfaces on the principal axis. Light ray passing this point is not deviated. Principal axis is line passing through optical centre of lens, perpendicular to lens. Principal focus (F) is the point on principal axis where deviated incident parallel light ray is made to converge. Principal focus occur on both sides of the lens with same focal length Focal length (f) is the distance between optical centre and principal focus. Focal plane is a vertical plane passes through principal focus; perpendicular to principal axis. Ray Diagrams – To construct one
Ray (1) leaves the tip of object parallel to principal axis, and refracted by lens and will ALWAYS passes through principal focus (F) on the opposite side. Ray (2) leaves the tip of object and passes through optical center undeviated. Ray (3) leaves the tip of object and passes through principal axis on the same side, and refracted by lens parallel to principal axis NOTE: The point where all the rays meet is where the object is formed. Two rays will do. The numbered rays are construction rays (rays that determine where the object will be formed).The actual rays is the shaded one (light cone), on which it ALWAYS passes the lens, and will not be out of the lens.
:::SOME RAY DIAGRAMS::: (1) O between 2F and infinity (behind 2F)
Image Characteristics Real Inverted Diminished
Location of Image I at opposite side of O – between 2F and F
(4) O at F
Applications Camera Human eye
Location of Image
Real (I other side of O) Virtual (I same side as O) Upright Magnified
Could be at same side as O or opposite side of O; both at infinity
Applications Same side: spot light Other side: telescope’s eyepiece
(5) O between C and F
(2) O at 2F
Image Characteristics Real Inverted Same size (3) O between F and 2F
Image Characteristics Real Inverted Magnified
Location of Image I at opposite side of O – at 2F
Location of Image
I at opposite side of O – between 2F and infinity
Projector Microscope’s objective lens
Image Characteristics Location of Image Virtual Upright I on same side as O Magnified Applications of Converging Lenses Camera
Applications Magnifying glass Long-sighted spectacles
Converging lens can be moved so that real, inverted, sharp and diminished image can be formed on the light sensitive film Shutter controls how long film is exposed to light and its intensity; diaphragm controls how much light pass through aperture
CHAPTER 14: ELECTROMAGNETIC SPECTRUM 14.1 PROPERTIES OF ELECTROMAGNETIC WAVES
Concave mirror in light guide reflects light from lamp to condenser lenses so that there’s no converging of light, where it directs light through reticle(slide) and converge to the projection lens. Projection mirror is moved forth and back to produce sharp, real, magnified image on screen. As the image is going to be inverted when it passes the projection lens, the film is set upside down and the image is projected upright. Magnifying Glass
It produces virtual, magnified, upright image. The image appears larger and more distant. The image cannot be formed on a screen.
END OF CHAPTER 13
Characteristics: Transfer energy from one place to another Transverse waves Can travel through vacuum Travel at the speed of light They have wave properties, i.e. refraction, reflection Have the equation v = f The electric and magnetic fields are perpendicular to each other and to the direction of travel of wave 14.2 APPLICATIONS OF ELECTROMAGNETIC WAVES Shorter wavelength higher frequency more energy Radio Waves Produced by oscillating electric currents in transmitter and received by another aerial antenna at the other end
LW, MW and SW are used for AM radio communication VHF is for high quality FM stereo radio & terrestrial television communication UHF is for terrestrial television communication Microwaves Are very short wavelength radio waves produced by klystron tube, used for:
Remote control Infra-red is produced by Light Emitting Diode (LED) in the unit which sends the instruction signal by amplifying it to the LED which later translates it into infrared radiation. The receiver’s sensor detects and analyses the signal.
Passive infra-red (PIR) intruder alarm Intruder’s body heat triggers the alarm as he passes the field view of the detector, which also causes sharp increase in infra-red energy. Gradual infrared energy increase will not trigger the alarm as it only detects rapid increase.
Satellite communication – mobile phone sends microwave signals to space while calling by aerial dish to communication satellites orbiting the Earth which later relay signals to the call destination Live telecast – same way as mobile phones
Visible Light Is the electromagnetic spectrum visible to human eye classified by colours ranging from violet to red.
Microwave – water particles in foods greatly absorb the waves carrying the heat energy which later heats up the food and cooks it very quickly Infra-red Radiation Waves beyond red end of spectrum, possessed by all objects The hotter the object, the wavelength gets shorter, red visible spectrum is seen Cooler object, the wavelength is longer, ordinary eye cannot detect infra-red They are used in: Infra-red camera Hot parts of objects emit more infra-red radiation of shorter wavelength affecting the camera film more. Therefore temperature difference can be detected by difference in brightness. Applications in: check healthy crop-sick ones emit different infra-red radiation to healthy ones checking missile installation-missile plants changes surface temperature
Thermogram Infra-red radiation emitted by the body is detected as hot spots by thermogram Malignant growth, i.e. cancer, arthritis – higher temperature, more radiation
LASER- Light Amplification by Stimulated Emission of Radiation, used for: Weld and cut hard materials Spot-weld detached retina Seal blood vessels Measuring a piece of road over large distances Sending digital signals by short laser light pulses through optical fibres. Ultra-Violet Radiation Waves beyond violet end of visible spectrum; main source: sunlight. Used for:
Stimulation of vitamin D production in body for healthy bones Excess may cause skin cancer and retinal damage Ozone absorbs substanial amount of UV rays to prevent excess UV
Sunbed UV rays carry sunlight energy which carries extra rise for suntans
Killing bacteria and viruses Operating rooms use UV to sterilise them and the surgical instruments
To kill cancerous cells To sterilise equipments Checking welds in metals
Low intensity UV lamps set above meat counters preventing meat going bad
Forgery checking Notes and bank signatures contain glow ink when exposed to UV radiation Fluorescent lamps coating Electric current causes gas inside the lamp tube to emit UV radiation. The UV is absorbed by chemical coating and white light is emitted.
DISADVANTAGE OF GAMMA RAYS: They penetrate very deeply and seriously damage when absorbed by living tissues. 14.3 EFFECTS OF ELECTROMAGNETIC WAVES ON CELLS AND TISSUES Exposure causes heating effects; Over-exposure causes pain sunburn/skin cancer EM wave consists of very small energy packets – photons. Shorter wavelength higher frequency more energy in each photon.
X-Rays Short electromagnetic waves produced when high energy electrons lose energy after striking metal target. Uses are:
Diagnostic tool in medicine and dentistry – to show structure of bones & teeth
Treatment for cancer
Examine hidden flaws and cracks of metal parts during welding
Inspecting appliances whether they have been properly assembled
Safety inspection in airports
X-ray photographs on painting pigments for forgery checking
DISADVANTAGE OF X-RAYS: High penetrating power could destroy living tissuesand organisms Gamma Rays Very short electromagnetic waves emitted by radioactive nuclei/during nuclear reactions. Uses are:
END OF CHAPTER 14
CHAPTER 15: SOUND 15.1 SOUND WAVES Sound is energy propagated in longitudinal wave such that the particles of medium, i.e. air, vibrate forth and back in a direction parallel to the direction of wave. It is produced by vibration of objects Propagation (Way A Wave Travel) of Sound Sond waves are produced when vibrating object alternately pushes and pulls the air adjacent to it, causing rapid small changes in air pressure.
Speed of sound differs in gases, liquids and solids – they have different interatomic forces strength and atom arrangement. Speed travels fastest in denser media. So, sound travels best in solids. Audible Frequencies Range for human ears: 20 Hz – 20 kHz Range sensitivity lowers as human grows older Sounds over the hearing limit – ultrasound Sounds below hearing limit – infrasound
Dog has higher audible frequency and can hear ultrasonic whistles Bats (10kHz – 120kHz) locate obstacles and prey in the dark by producing sound waves which echoes on any obstacles which is then heard by bats
15.2 SPEED OF SOUND Velocity (v) = (b) When prongs move outwards, layers of air are pushed close together so that a compression of air particles is formed. The disturbance is passed from particle to particle, causing compression move outwards. (c) When prongs move inwards, layers of air are pulled apart causing decompression of air particles called rarefaction. Compression – high pressure region in air caused by disturbance of air particles close together. On sinusodial wave is the crest. Decompression – low pressure region in air caused by layers of air pulled apart. On sinusodial wave is the trough. Transmission of Sound Through a Medium Sound must travel in a meduim as there should be a material to be compressed or stretched. So, sound cannot travel in vacuum The bell is rung in vacuum. Will you hear it?
Example: Two observers are at A and B 1000m apart. A steady wind blows from B to A. When a pistol is fired from A, observer at B recorded the interval between the time he saw the flash and the time he heard the sound as 2.34 s. When it’s fired at B, the time interval was 2.11 s. Calculate the speed of sound in air and the speed of wind BA. Sound speed = v, Wind speed = vw v - vw =
sound speed subtracted to wind as wind reduces the sound speed
= 427.3504 m s-1............................................................(1) v + vw = sound speed added to wind as wind increases the sound speed = 473.9336 m s-1.............................................................(2) (1) + (2) 2v = 901 m s-1 V = 451 m s-1 sound speed (2) – (1) 2vw = 46.5832 vw = 23.2916 m s-1 wind speed
15.3 ECHO Echo is the reflection of sound when it hit large hard surfaces, heard after an interval of silence. Reverberation is the prolonged sound of source due to the reflected sound follows closely behind the original sound, and is affected by close position of source
15.5 ULTRA SOUND It is a sound wave with frequency greater than 20kHz. Applications of ultrasound:
Ultrasonic scanning of women’s fetus and abnormal growths Ultrasound is sent into patient’s body and it is then reflected Reflected ultrasound is detected and monitored, and the computer constructs the image of the reflected signals. Internal tissues and organs are shown.
Measurement of speed of blood flow with ultrasonic flow meter
Shock wave lithoripsy for breaking kidney stones
Locating object distances by sonar Ultrasound pulses are generated by sonar apparatus and then echoed and picked up by detector. To measure the distance, use echoloctaion formula. Used in: ships to detect fishes or sunken ships; autofocus cameras measuring distance for focus adjustments
Cleaning of small, intricate items Small items are placed in liquid and ultrasonic high-frquency vibrations loose out dirt and corrosion
Steel rollers Ultrasound is emitted and change is detected by detector, representing change in steel thickness. Detector send signals and adjusts gap between rollers for suitable thickness
Using Echoes to Find Distances – Echolocation Velocity of sound (v) = Example: Observers A and B stand 50m in front of an obstruction and A claps 50 times continuously every time he hears an echo. B records the time and finds that the interval for first to fifty claps is 14.5 s. What is the speed of sound? Time interval between each clap:
= 0.29 s
velocity = = 345 m s-1 15.4 PITCH AND LOUDNESS OF SOUND Pitch and Frequency Pitch is a sound property which distinguishes the way a sound sounds. Higher frequency = higher pitch Pitches in musical instruments Guitars, pianos and violins – the longer the string, the lower the frequency Flute – the more holes closed, the lower the frequency The air column vibrates longer when the holes are closed Drums – smaller drum surface, higher frequency produced Loudness and Amplitude The more an object vibrates, the higher the amplitude, the louder the sound, although they are all of the same frequency.
END OF CHAPTER 15
PHYSICS GCE O LEVEL SYLLABUS 2010 THEME 5: ELECTRICITY AND MAGNETISM Name: ________________________________ Class:__________ CHAPTER 16: STATIC ELECTRICITY 16.1 LAWS OF ELECTROSTATICS Two charges – negative and positive Negatively-charged Amber rubbed with fur Rubber rubbed with fur Polythene rubbed with wool
Charging by Induction Induction – production of electric charge on surface of conductor under electric field influence. Two types – Induction and Earthing Induction
Positively-charged Glass rubbed with silk Perspex rubbed with wool
Basic Law of Charges Cause and Effect Like charges repel Unlike charges attract each other
Example (charged amber with charged rubber) (charged glass with charged amber)
SI Unit – coulomb (C) Equation: Charge (Q) = Current (I) x Time (t)
(a) The spheres are neutral and in contact with each other. (b) When negatively-charged rod brought near sphere P, electrons from P are repelled and conducted up to the other end of sphere Q. On the other hand, positive charge from Q and P are attracted to end of sphere P closer to the rod. Thus P possesses positive charge while Q possesses negative charge. (c) Sphere Q is moved away from P in presence of rod to keep position of charges. (d) Rod is removed. P and Q possess same number of opposite charge.
16.2 PRINCIPLES OF ELECTROSTATICS Charging by Rubbing
Earthing Obtaining Positive Charges by Earthing Process
- First, both objects neutral (number of positive and negative charges are same). - When polythene rod is rubbed with wool, electron is transferred from wool to polythene rod, due to movement of electrons with the help of friction. - Electrons that were originally part of wool are separated from their atoms and deposited onto polythene. - Wool, in return, lost the same number of electrons, therefore negatively charged. - Atom loses electrons – positive ion; atom receives electron – negative ion
(a) Negatively-charged rod brought near Q; repelling electrons to the other side of Q, leaving positive charges attracted to the rod at the end of Q nearer to the rod. (b) By earthing by touching Q, electrons are further repelled to the Earth. (c) Hand is removed in presence of rod P to keep the charges. (d) P is removed after hand is taken away, leaving the conductor positively charged.
Obtaining Negative Charges by Earthing Process
(a) Positively-charged rod brought near Q; repelling positive charges to the other side of Q, leaving electrons attracted to the rod at the end of Q nearer to the rod. (b) By earthing by touching Q, the circuit is closed, allowing electrons flow from Earth to neutralise positive charges at Q. (c) Hand is removed in presence of rod P to keep the charges. (d) P is removed after hand is taken away leaving the conductor negatively charged. WHAT IF? What if only one body is induced without earthing? - When charged perspex rod brought near a neutral paper, negative charge is induced at the end of paper near rod, while positive charge is repelled to other end. - The attraction creates upward force F1 while repulsion creates downward force F2 - Attraction is greater than repulsion, thus F1 greater than F2, moving the paper towards the rod. - As paper touches rod, negative charges are induced to rod, making paper positively-charged. - Same positive charges repel, thus paper now repelled from the rod. * Vice versa happens when rod is negatively charged, yet paper will still attracted then repelled. 16.3 ELECTRIC FIELD Electric field is a region which electric charge experiences a force Electric field line is the path a positive charge would take if it is free to move - The direction of the line means the direction of force acting on positive test charge.
-q +q - For a positive point charge, the lines moves radially outwards to all directions. - For a negative point charge, electric field lines moves radially towards the charge. *The nearer the lines to the charge, the stronger the electric field* ELECTRIC FIELD LINE RULES - Must begin from a positive charge moving outwards and end on negative charge. - Number of lines drawn leaving positive charge or ending negative charge is proportional to the magnitude of the charge.
- No field lines cross each other. Different responses of the meeting of 2 charges
Nasty Electrostatics REFUELLING AIRCRAFT Look at the picture below of a jet being refuelled. A thin copper wire is attached from aircraft body touching the ground. Why would there be such a wire?
- As fuel is transferred to aircraft with hose, it rubs against hose and acquire lots of negative charges. The hose transfers electrons to the petrol and hence acquire positive charges. When these two charged objects are in contact, the opposite charges may recombine and produce sparks which easily ignites the petrol. - Charges are discharged by earthing with a thin copper wire which carry electrons from ground to neutralise the charges on the hose before charges are built up and cause sparks.
PANTS ON FIRE - Synthetic fibres in clothing are insulators which are easily charged by rubbing. In case of dry air blowing, these fancy distro may catch fire.
Is the same process as photocopier but step 2 is different. After that all the same. - In step 2, command is sent from computer to printer to shine laser beam onto rotating drum to “draw” exact patterns from document as electrical charges.
Helpful Electrostatics PHOTOCOPIER
ELECTROSTATIC PAINT SPRAYING Aim: To evenly coat car parts even to the most inaccessible parts. - Paint droplets from aerosol is charged by rubbing againts spray nozzle. - Car body is earthed, paint droplets will be attracted onto metal body. - Since all droplets have same charge, they repel and distribute themselves evenly. ELECTROSTATIC PRECIPITATOR
- Selenium drum is positively charged by rotating it near highly charged metal wire - Strong light is reflected off the page and projected onto drum. White parts of the paper reflect intense light on drum. Since selenium becomes electric conductor when receive light, the part receiving light conducts electricity and become discharged. Other coloured parts of paper receive no light and since selenium becomes insulator when it’s in darkness, the positive charges remain in position. The position of these charges creates the same pattern as the original document. - Negatively-charged toner is sprayed onto the drum and gets attracted to the positive charge pattern. This creates the image of the original. - The toner which has been patterned is transferred onto paper as drum rotates. - Heat is applied to paper to melt toner so that it is fixed onto the paper surface.
Aim: To clean smoke out from chimney by collecting ash and dust in precipitator. - When smoke particles move past negatively-charged grid, they become negatively charged and get attracted to the positively charged plates. As a result, only waste gases are out of chimney. This method efficiently collect 99% smoke. Note: Only smoke are collected but harmful gases are still free. END OF CHAPTER 16
CHAPTER 17: CURRENT OF ELECTRICITY 17.1 CONVENTIONAL CURRENT AND ELECTROMOTIVE FORCE Conventional Current Electric current – the flow of electric charge from one place to another Current (I) is the rate of flow (t) of charge (Q) I= SI Unit for current = Coulomb per second (C s-1) (or) Ampere (A) Flow of charges can be positive, negtive or both Conventional current moves to the direction of the flow of positive charge In electrical circuitry, there is no positive charge but electron flow so the direction of conventional current is opposite ti the direction of electron motion. Example: A charge is created by a Van de Graaf machine which takes 10-3s to flow past a galvanometer. The galvanometer reads a current of 1A (nanoamperes). Calculate the total charge created by the machine and the number of electrons passing through galvanometer/second (charge/electron=1.6 x 10-13C) Charge: Q = It
= 10 A x 10 s = 10-9C
= 6.25 x 10
Cells arranged in series has: - Total current the same across all cells in each branch, i.e. 0.6A - Total voltage is the sum of V1, V2 and V3, and in this instance is 4.5V Cells arranged in parallel has: - Total voltage the same across all cells in each branch (i.e. 1.5 V) - Total current is the sum of I1, I2 and I3, and in this instance is 1.8A Measuring: Current is measured by ammeter in series in the circuit. Unit is ampere(A) EMF is measured by voltmeter directly across the d.c. source in a circuit. Unit is volt (V)
17.2 POTENTIAL DIFFERENCE Potential Difference(V) – work done (W) to drive a unit charge (Q) across a component
Electromotive Force (e.m.f.) E.m.f.(E) – work done (W) by source driving a unit charge (Q) around the whole circuit E= SI Unit for current = joule per coulomb (J C-1) (or) Volt (V) CURRENT AND ELECTROMOTIVE FORCE (E.M.F.) Arrangement of Cells
V= SI Unit for potential difference = joule per coulomb (J C-1) (or) Volt (V)
Potential Difference Across a Circuit The sum of potential difference across the whole component in a circuit must be equal to the sum of e.m.f of the cells as potential energy gain from cells lose the energy as pass through a component to convert into other form of energy. E1 + E2 + ... = V1 + V2 + ... Example: The potential difference across a light bulb in a circuit is 5V. Calculate the current flowing throught the bulb if the time for the current to pass the bulb is 0.8s and the energy dissipated was 30J. V= From Q = It, V= W = Vit 30J = 5V x I x 0.8s I= = 7.5A 17.3 RESISTANCE Resistance (R) – the ratio of potential difference (V) across a component to the current (I) flowing across it. R= SI Unit for resistance = ohm () CHAPTER REVIEW 1. A filament bulb, F1, has a resistance of 1 . It’s was connected solely across a circuit with a 3.0V d.c. supply. (a) (i) Briefly explain the meaning of “...has a resistance of 1 ”. (ii) State the potential difference across the filament bulb. Explain your answer. (iii)Hence, calculate the current flowing past the bulb. (b) Another filament bulb, F2, was placed in a circuit, but now parallel across F 1. Explain, if any, the differences in
(i) the current, (ii) the voltage, (iii) the resistance, of F1 after the installation of F2. 2. A student installed component X across a circuit. He then judged that this component did not obey Ohm’s law. (a) Define Ohm’s Law. (b) Suggest, by illustrating an experiment, how the student came to the conclusion of component X. (c) The graph of p.d. against current of X looks like Figure 17.8. Suggest component X.
Copyrights AF/PS/2009/2010 CHAPTER 18: D.C AND A.C. CIRCUITRY
28 CHAPTER 19: MAGNETISM 19.1 MATERIALS AND MAGNETS Magnetic materials are materials which attract to magnets, e.g. iron, cobalt, alnico, steel Non-magnetic materials are materials which aren’t attracted to magnets, e.g. copper, wood Permanent magnets are magnets that retain their magnetism for a long time Temporary magnets are magnets that lose their magnetism easily 19.2 PROPERTIES OF MAGNETS 1. Poles of a magnet are each located at the ends of a magnet. 2. When a bar magnet comes to a rest, one end of the magnet will face North, called North-seeking pole/North Pole, while the other end faces South, called South-seeking pole/South Pole. 3. When S-pole of a magnet is brought towards N-pole of another suspended magnet, they will attract. But if N-pole is brought towards the N-pole of the suspended magnet instead, the suspended magnet will move away from the incoming magnet, showing repulsion. This is an important law “unlike poles attract, like poles repel”. Testing whether one is a magnet / magnetic material To test if the subject is a magnetic material When brought near magnet, subject will be attracted to both N-pole & S-pole of the magnet. To test if the subject is a magnet When brought near magnet, subject will be attracted to one end and at the other end, it will be repelled. To test if the subject is a non-magnetic material When brought near magnet, subject will remain stationary when brought to either poles.
arrangement of tiny magnets. To prevent this we use two soft-iron keepers placed across a pair of magnets.
MAGNETISATION AND DEMAGNETISATION MAGNETISATION When an unmagnetised magnetic material is brought near a permanent magnet, it is attracted to either poles of a magnet and becomes a magnet itself, with the pole near to the point of contact with permanent magnet induced with opposite pole to pole of permanent magnet at the point of contact while the other end of the magnetic material has same pole as the pole on the magnet at the point of contact. This is induced magnetism. When another magnetic material is brought near the induced magnet, it will have the same polarity (i.e. polar position) as the induced magnet above it. To test this theory, bring a magnet with its pole the same as the polarity of the permanent magnet at the point of contact brought near to the magnetic material and it will bring about reflection. Theory why magnetism occur If we cut a piece of magnetised steel bar into pieces, each piece will still be a magnet with N-S pole the same position as each other. This is because the magnet is made up of lots of tiny magnets with the N-poles pointing the same direction. At the ends of the bar, the tiny magnets spread out due to repulsion of between poles.
In an unmagnetised steel bar, the arrangement of tiny magnets points at random direction causing the polar effect by the tiny magnets cancel each other out. The more tiny magnets aligned in the same direction, the stronger the magnet is. Also, if we put magnets side by side, the magnets weaken faster because the free repelling poles near the ends of the magnet repel each other, hence distrupting
1. Stroking method The unmagnetised bar is stroked the same way several times with permanent magnet with magnet lifted up high enough at end of each stroke. The end of bar where stroke finishes has opposite pole to the end of the magnet in contact. 2. D.C. method A solenoid (cylindrical coil) is wound around a cardboard roll and the steel bar is inserted inside the cardboard roll. Polarity of the steel bar can be found by: (i) Direction of current at the ends of solenoid Look at one end of solenoid and if the current is flowing in anti-clockwise direction, it’s the N-pole. If the current is flowing in clockwise direction, it’s the S-pole. Repeat the experiment for the other end of the solenoid. (ii) Right-hand grip rule By using right hand gripped onto solenoid, the fingers show the direction of current flow in solenoid and the end of steel bar thumb points to is N-pole.
DEMAGNETISATION 1. Heating Heat a magnet until red hot and lay it east-west. Heating increases vibrations of atoms of magnet causing the tiny magnets to lose their alignment. Hence magnetisation is lost.
2. Hammering Hammer magnet & lay east-west direction. It destroys tiny magnets alignment 3. A.C. method Place the magnet in solenoid with low voltage a.c. supply. Slowly remove the magnet from the solenoid in east-west direction while current still flows.
In (b) and (d), when two magnets of equal strength are placed with same poles facing each other, magnetic field effects are cancelled out, forming a point where there are no magnetic effect on X, called the neutral point. Compass placed here points in uncertain direction.
19.3 MAGNETIC FIELD Magnetic field is the region around magnet where magnetic force is exerted Plotting Magnetic Field
Place magnet on a paper so that N-pole directs to North and S-pole directs to South. Place a small plotting compass at A near the pole of magnet. Mark the ends of the compass needles with dots 1 and 2. Compass is then moved to B with one end of compass needle, in diagram is South end, exactly on dot 2. Dot 3 is marked on the other end of compass needle. Repeat the steps until the compass reaches the other pole of the magnet. Join the dots formed to obtain magnetic field lines and the direction is from N to S pole. Laws of magnetic field 1. Magnetic field lines should NEVER cross each other 2. Outside magnet, magnetic field lines start from N-pole to S-pole. Inside magnet, magnetic field lines continues from S-pole to N-pole, forming continuous loops. 3. The lines which are closer to each other represent stronger magnetic field. Straight parallel lines of force represent uniform magnetic field. Magnetic field patterns When two magnets are brought close to each other, the field produced is the result of combined effects of the magnets. In (a) and (c), when two magnets of equal strength are placed with opposite poles facing each other, magnetic field becomes stronger.
19.4 TEMPORARY AND PERMANENT MAGNETS Magnetic Properties of Iron and Steel
A steel bar and iron bar of same dimensions are placed to be magnetised by bar magnet on top of them by induction. Iron bar attracts more iron filings than steel bar, indicating it’s magnetised easily and stronger than steel bar. However, when bar magnet is removed, iron filings from the iron bar all fall off, but only some iron filings from the steel bar fall. This proves iron loses magnetism more easily Magnetic materials which are harder to magnetise but retains its magnetism longer are hard magnetic materials. Magnetic materials which are easier to magnetise but loses its magnetism easily are soft magnetic materials.
Applications of Magnets 1. Magnetic shielding When a soft magnetic material (e.g. iron) is used to cover an object sensitive to magnetic field is placed in areas of strong magnetic field, instead going through object, iron provides path for magnetic field to move through its volume and exits via other edge. Hence no magnetic field inside iron. Iron used because it’s easily magnetised.
2. Galvanometer Coil suspended in magnetic field of permanent magnet in galvanometer will be moved due to deflection created by turning effect produced in coil when current flows into and out of the coil.
3. Magnetic door catch Magnetic strips fitted to doors of refrigerators keeps the doors closed by attraction.
4. Also used in: D.C. motors, loudspeakers, resetting metal index in Six’s thermometer, removal of small metal objects from eyes, memory chips
CHAPTER 20: ELECTROMAGNETISM Before we start Electromagnet consists of solenoid of many turns wound on core of soft magnetic material The strength of a magnetic field is increased by: - Increasing the number of turns of solenoid - Passing larger current through solenoid - Inserting soft magnetic material as a core
For creation of force by current source, we use Fleming’s Left Hand Rule. For creation of current source by force, we use Fleming’s Right Hand Rule. Current flowing out of page is denoted byʘ but into page is by . For determining the magnetic field across a solenoid, we use Right Hand Grip Rule. 20.1 MAGNETIC FIELD BY CURRENT When a compass is placed under current-carrying wire, it deflects and when placed above the wire, it also deflects, but to opposite direction. This shows magnetic field is produced. Magnetic Field Due to Long Straight Wire By placing a wire vertically through a horizontal card and place iron filings around it, we know the pattern of magnetic field around a straight wire. The iron filings are closer to each other when placed nearer to wire, showing stronger magnetic field. It is thus known that when we increase the current, more magnetic field lines are formed, creating stronger field. To find out the direction of magnetic field, we use plotting compass placed along line of magnetic field. Diagrams below illustrate this.
We can also deduce the direction of magnetic field by using the right-hand grip rule. It is known that when the current is reversed (e.g. from into page to out of page), the direction of magnetic field is also reversed. Magnetic Field of a Flat Coil Magnetic field due to current by flat coil is stronger inside coil than outside because field from each wire side are concentrated in a small area. They’re also straight and perpendicular to plane of coil.
Right Hand Grip Rule Use your right hand fingers to curl around the wire and your thumb pointing towards the direction of current. The direction of the curled fingers is the direction of magnetic field.
Magnetic Field of a Solenoid The magnetic field lines resembles that of a bar magnet. Inside the solenoid, it resembles field lines in flat coil. It even has poles. To determine the polarity, look at one end of solenoid and if current is flowing in anti-clockwise direction, it’s N-pole. If current is flowing in clockwise direction, it’s the S-pole. Repeat the experiment for the other end of the solenoid. Otherwise, use right-hand grip rule in FIGURE 19.5. It is known that if we reverse the current, the polarity will also be reversed. Applications of Electromagnets 1. Magnetic Relay
It consists of 2 circuits – one consisting of electromagnet to switch on another circuit. When first circuit is closed, current flowing through solenoid magnetises the iron core which then attracts the soft-iron armatur. The upper part of armature swings up and touches the contact hence closing the second circuit. The second circuit may need large current to operate, hence an electromagnetic relay can activate the second circuit by just using a small current for the first circuit. 2. Reed Switch A reed switch is a pair of soft iron strips, known as reeds, housed inside glass tube, containing inert gas (to prevent oxidation of the reeds), with a gap between reeds. When magnetic field from bar magnet/electromagnet is brought near, say the glass is wound, reeds become temporarily magnetised and attract each other, closing contacts and allows current flowing in circuit connected to the reed switch 3. Electric Bell When switch’s on, circuit’s closed & current flows through electromagnetic coil. Soft iron cores are magnetised & armature is attracted to the cores so that the hammer strikes the bell. As soon as the armature moves towards the core, the circuit breaks and hence the armature returns to original position as cores lose their magnetism. The return of armature closes the circuit and therefore current flows again and repeats process. The bell continues to ring as long as switch is kept on. 4. Circuit Breaker Circuit breakers are used to cut circuit when current exceeds specified value. When usual current’s flowing, strength of electromagnet is insufficient to separate contacts. When current’s too high, strong magnetic force pulls contacts & breaks circuit. Spring keeps contact while fault’s repaired. Contacts stay apart unless contacts are pushed back by pressing reset button.
5. Audio/Video Tapes The tapes are coated with magnetic material. Sound/pictures are represented as varying currents. The currents causes electromagnet at the head of the tape to magnetise tape according to the picture or sound. Force on Current-Carrying Conductor in Magnetic Field The direction of force on conductor can be determined using Fleming’s Left Hand Rule. Look at the diagram below. Thumb shows direction of force, first finger shows direction of magnetic field and second finger shows direction of current. Position the first finger to direction of magnetic field and your second finger to direction of current flow. The thumb will show you where the force directs the conductor.
An explanation A current-carrying conductor produces a circular magnetic field. Between two magnets there is a magnetic field produced from North to South pole. When the current-carrying conductor (e.g. wire carrying current) is brought between the magnetic field of the 2 magnets, the magnetic fields created will combine to form a stronger magnetic field.
Magnetic field will combine when the direction of the magnetic field is the same to produce stronger field. Contrawise, they repel to produce weaker field. Magnetic field created by wire has one side which coincide with the direction of the magnetic field. This side attracts the magnetic field to take this path, producing stronger magnetic field. Otherwise, the sides which don’t coincide has weaker magnetic field. Force is exerted on the conductor from the region where field is now stronger to the region where field is now weaker to balance the unequal fields. Force Between Two Parallel Current-Carrying Conductor Just remember: Like current directions attract. Unlike current directions repel. ...and also apply the theory on force on current-carrying conductor in magnetic field.
20.2 MAGNETIC FLUX OF D.C. CIRCUITS Turning effect on Current-Carrying Coil
We have learnt force between two parallel current-carrying conductor is due to attraction/repulsion between magnetic fields created by both wires. Now, that there’s a magnet by the side of these two current-carrying conductor, flowing in opposite direction and affiliated by coil, what would happen? Look at Figure 20.12. In (a), two parallel current-carrying coil placed between a horseshoe magnet create circular magnetic field for each side. Applying Force on Current-Carrying Conductor in Magnetic Field, the side of each fields coinciding with magnetic field of horseshoe magnet will merge and create an equal but opposite force on each side of the coil, which is called catapult field. The combination of these forces will rotate the coil. D.C. Motors
When circuit is closed, conventional current flows from positive terminal of battery towards X through P, then through coil and back to battery through Y and Q. To determine the direction of turn of d.c. motors, we use FLEMING’S LEFT HAND RULE on EACH SIDE OF THE COIL, then UPWARD-SIDE OF COIL TURNS TOWARDS DOWNWARD-SIDE OF COIL. For example, in the diagram, upward force is experienced on right side of coil while left side of coil experiences downward force. The coil hence turns anticlockwise until it reach vertical position, where at this point current is cut because split-ring is not in contact with carbon brush. However, the momentum of the coil continues the rotation until the split-rings is, again, in contact with carbon brush. Note that half-ring Y is now in contact with P while X is now in contact with Q, The process is then repeated. Note also that the current in coil reverses each time coil passes vertical position, i.e. the right side of coil flows towards the battery at first, but now it’s on the left side and current now flows away from the battery. Turning effect can be increased by: 1. Increasing number of turns in coil, e.g. giving extra force to increase period 2. Increasing magnitude of current 3. Inserting soft iron core within coil to concentrate magnetic line of force. This will create a radial field which keeps the pair of forces acting on coil constant and increases magnetic field strength hence increasing turning effect in coil,
D.C. motors works only with direct current. It consists of a coil of wire, which spins on an axle, placed between two N-pole and S-pole of a permanent magnet, and connected to a split-ring commutator, which, each half of the ring rubs against carbon brush as the coil turns to allow flow of current.
Copyrights AF/PS/2009/2010 20.3 CURRENT BY MAGNETIC FLUX 20.4 MAGNETIC FLUX OF A.C. CIRCUITS CHAPTER 21: INTRODUCTORY ELECTRONICS 21.1 CATHODE RAY OSCILLOSCOPE 21.2 CIRCUIT COMPONENTS
CHAPTER 22 – ELECTRONIC SYSTEMS 22.1 Logic Gates RECALL! Mathematics “D” Chapter - PROBABILITY We use “1” to indicate that the action is “true” and “0” if the action is “false” Generally, A and B are represented as inputs while Q is represented as output Gate Name Symbol Truth Table Definition in words A Q Output is the opposite of input, i.e. when input is NOT Gate 0 1 high output is not high 1 0 A B Q 0 0 0 Output is high if one OR OR Gate 0 1 1 more inputs are high 1 0 1 1 1 1 A B Q Output is high if input 0 0 0 AND Gate „A‟ AND input „B‟ are 0 1 0 high 1 0 0 1 1 1 A B Q Output is NOT high if 0 0 1 NAND Gate input „A‟ AND input „B‟ 0 1 1 are high 1 0 1 1 1 0 A B Q Output is NOT high if 0 0 1 NOR Gate one OR more inputs are 0 1 0 high 1 0 0 1 1 0 In electrical circuitry, “1” means a high input/output level of voltage (+5V) while “0” means a low input/output level of voltage (0V). A Logic Gate produces a single logic output from one or more logic inputs.
NOT Gate A NOT gate will produce an opposite output value from the input. OR Gate An OR gate produces high output level when either inputs are high. The input on any input slots must be greater than zero to achieve high output. AND Gate An AND gate only produces high output level if both inputs are greater than 0 NAND Gate This is a combination of NOT gate and AND gate. In other words, we can imagine that this is NOT an AND gate and the output of the gate is opposite to the AND gate, i.e. Output is high if both inputs are NOT greater than 0. NOR Gate This is a combination of NOT and OR gate. We can say that this is NOT and OR gate and that the values of outputs are the opposite to that of an OR gate, i.e. Output is high if any input slots are NOT greater than 0. EXERCISE: A connection is made from a circuit to the inputs A and B of a NAND gate and the output of the NAND gate is connected to an LED and a resistor as shown in the figure below.
(a) Draw the truth table for a NAND gate.  (b) The LED now lights up. State the inputs A and B of the gate and explain why the LED lights up.  (c) Metal conductor X is slowly heated to a very high temperature. At a certain temperature, the LED is switches off. Explain why this happens [Physics GCE O Level Oct/Nov 09]
CHAPTER 23 – ATOMIC PHYSICS 23.1 Radioactivity Radiation has an ability to ionize gases. Radioactive substances emit 3 kinds of radiation: (a) Alpha(α) –rays (b) Beta(β) –rays (c) Gamma(γ) –rays Detection of Radioactivity 1. Gold-leaf electroscope As a radium source is brought near cap of negatively-charged electroscope, radiation emitted by radium source ionizes air molecules above cap. As cap is negatively-charged, negative ions are repelled while positive ions are attracted to cap. These ions neutralize negative charges on the cap and the gold leaf thus collapses.
2. Diffusion cloud chamber Air containing alcohol vapour in a chamber is cooled with dry ice placed below a thin black metal plate. When radioactive source is introduced into the chamber, the radiation produced passes through the vapour leaving white tracks on black plate in the dense vapour due to condensation of alcohol vapour on ions formed.
The table shows how the tracks tell what kind of radiation was introduced. Radiation Tracks made Characteristics α–particles
Tracks are straight, short and thick; proving that radiation is strongly ionizing Tracks are twisted, thin and long; proving that the radiation is less ionizing than α–particles. The twisted nature is because β–particles are easily deviated by collisions with vapour molecules. Tracks are short, thin and irregular; proving that the radiation is least ionizing.
3. Geiger-Müller (GM) tube When ionizing radiation enters the tube by penetrating the thin mica window, argon atoms will ionize to electron and argon ion pairs. The free electrons will accelerate towards fine wire anode placed parallel between 2 cylindrical cathodes. The accelerating electrons will cause further ionization of argon atoms by colliding with them, producing many electrons collected on anode. Positively-charged argon ions will attract towards cathode and the collection of electrons and argon ions at the electrodes produces pulse which is amplified and fed to a ratemeter (Refer OCR for link of pulse) which has grids marked in counts per second from which average pulse rate can be read. When the radioactive source is removed, a continuing register but low pulse rate is read on the GM tube, which is called background count caused by background radiation. Background radiation is caused by contamination of detector or its surrounding; or by the cosmic radiation entering Earth atmosphere from outer space. In experiment, we omit the low reading of background count.
The characteristics of 3 kinds of radiation Types of Radiation α-particles Positively-charged Nature of radiation helium nucleus Large amount of ionization (many Ionising effect ions are dissociated)
β-particles High-energy electrons Small amount of ionization
γ-particles Short EM wave (neutral) Negligible amount of ionization 10000 – very penetrating (can be stopped by 2cm lead)
100 – moderate penetration (can be stopped by 5mm wood) Deflected due to Deflected due to like Deflection in like negativelyUndeviated positively-charged magnetic and charged (neutral) particles electric field particles A little less than 107 ms-1 3 x 108 ms-1 Speed 3 x 108 ms-1 Ionization is the removal of electrons from a neutral atom to dissociate into electrons and positively-charged ions. Relative penetration
1 – Least penetrating (Can be stopped by a sheet of paper)
23.2 Half-Life Radioactive Decay It is the process when a group of unstable nuclei disintegrate to become more stable. Since it is not affected by chemical combinations or external conditions, radioactive emissions occur randomly over space and time, i.e. we cannot predict which nucleus and when electrons will disintegrate. To show that radioactive emission occurs randomly over space Position a few GM tubes, all equidistant from a radioactive source. The count rates on each GM tube will not be the same. To show that radioactive emission occurs randomly over time Place a GM tube near a radioactive source with long half like and determine the disintegration over a minute, which will tell us count rate. Repeat experiment a few times and since radioactive has long half life, the count rate should be same but the readings show slight fluctuation. Half-Life Half-life is the time taken for half of the unstable nuclei to decay. Let‟s compare ten million radioactive sodium nuclei with half-life of 15 hours with ten million radioactive radium nuclei with half-life 1600 years. It will take 15 hours for 5 million sodium nuclei to decay but 1600 years for radium nuclei to decay (half the amount) The table shows sample count rate of a radioactive substance. Half-life is 7.5 hours. 5000 2500 1250 625 312.5 Count rate/min 0 7.5 15 22.5 30 Time/h
26.3 Radiation: Applications, Hazards, Precautions The applications 1. Tracers The ability of detectors to measure small concentration radioactive material can be used to: - Find out the function of thyroid as the rate of radioactive iodine-131 applied on the thyroid to accumulate in it. - Find torn parts in moving components of machinery by applying radioactive isotope on surfaces of moving parts to find out how much of the radioisotope is rubbed off. - Find leaks in underground pipes as leaks emit an unusually high count rate on GM detector at area of leak. - Find how well plants absorb phosphate by radioactive phosphorus-32. 2. Penetrating radiation - Gamma rays can photograph deep inside engine to check any faults. - Gamma rays can be used to check constant thickness of rolled metal sheets. The rays is radiated from a source at one side of the moving sheets and on the other side, there‟s a ratemeter to find out count rate which depends on amount of radiation passing through steel plates. When plates are thick, low count rate and vice versa. The count rate is constant when the steel plates have equal thickness. - High penetrating power of gamma rays is used to kill bacteria in frozen or prepackaged foods to sterilize food and prevent food poisoning. 3. Power sources - Uranium-235 is used as fuel in nuclear power stations (Refer chapter 24)
- Some fire alarms emit α-particles to keep air around them slightly ionized so that any changes in level of ionization caused by smoke can be detected and the alarms go off. 4. Medical uses Gammatron decays radioactive cobalt-60 to emit β-particles and γ-rays. When properly shielded, γ-rays can be brought to bear on deep cancerous growths in a cancer patient and the radiation kills the cells of tumor. 5. Archaeological dating Radioactive carbon-14 isotope is present in air. When animals breathe in these, they become slightly radioactive. When they die, the carbon inside them will start to decay. The half-life of carbon-14 is almost 5500 years, so the age of dead animals can be found by comparing activity of carbon-14 in dead animals with a living one. The activity of the carbon in living animals is constant as it‟s continuously replenished while the carbon in dead animals is not replenished. The hazards 1. Overexposure - Radioactive radiation overexposure result in radiation burns, lead to sores & blisters for long time. Sometimes, this cause radiation sickness leading to death. - Radioactive radiation can lead delayed conditions, e.g. eye cataracts/leukemia may appear many years later. 2. Genetic mutations - The ionizing radiation cause genes to be destroyed or mutated leading to offspring with physiological and other abnormalities. 3. Radioactive leakage - Accidents which may cause leakage of radioactive materials into the air can pose health problems to people, livestock and plants.
The Precautions To prevent overexposure/accidents, the following measures must be taken: (i) Workers working with γ-rays must wear film badges or pocket dosimeters to keep track of accumulated dose of radiation they are exposed at a time. (ii) Always keep radioactive sources in lead-lined boxes kept in storage rooms built with lead bricks of 1m thick labeled with “Radioactive Material” as radioactive radiation do not penetrate thick lead. (iii) Radiation symbol must be displayed whenever radioactive radiation experiment is conducted. (iv) Persons doing experiments should use special protective coating such as leadlined suits and lead-lined gloves, holding the radioactive source with tweezers. At the end of the experiment, the contaminated clothing MUST be changed. (v) Food and drinks are prohibited when radioactivity experiment is made as radioactive dust contaminating food may be taken into the body. EXERCISE Below is half-life curve for mercury. The count rate is given in percentage.
(a) Calculate the half-life of mercury-203 (b) 120g of this mercury sample was left from January 1 until June 30. What is the approximate mass of mercury on June 30 as it decays? (c) Will the mercury be totally used up over time? Explain your answer. Two radioactive radiations, alpha-particles and gamma-rays, are emitted from a radioactive source. Explain (a) how a Geiger-Muller tube calculates the count rate of this radiation. (b)how you would prove that the radioactive radiation emitted were alpha-particles and gamma-particles. A 200 g sample of lawrencium is left in a container from 8:00 AM one morning until 2:00 PM the next afternoon. If the mass of the sample was one-eighth its initial mass, what is the half-life of lawrencium? END OF CHAPTER 23
CHAPTER 24 – NUCLEAR PHYSICS 24.1 Discovery of Nuclear Atom Geiger-Marsden experiment Geiger and Marsden conducted an experiment by aiming a beam of α-particles at a thin piece of gold foil. Most of them passed straight through gold foil while a small fraction of α-particles bounced back towards the source or deflected and struck onto ZnSO4 screen mounted on rotatable microscope for detecting α-particles (It shows a small flash of light whenever α-particles strike the screen.) Conclusion: Rutherford Atomic Model Rutherford proposed an atomic model that shows an atom is made up of dense core called nucleus, where positively-charged particles and most mass of the atoms are concentrated in here. It is surrounded by a circular orbit of equal number of electrons as the positively-charged particles since the charge of an atom is electrically neutral, i.e. 0. The nucleus and electrons occupy only 1 x 10-12 volume of atom, therefore an atom is mostly empty space. Explanation A small number of α-particles (positively-charged) are deflected as they are repelled by strong repulsive force of positively-charged nucleus when they pass through the atoms too close to the nuclei. Since most part of atoms is empty spaces, most of the particles can pass through undeviated.
24.2 The Structure of an Atom Atomic Model An atom contains: - Nucleus, consisting of protons (positively-charged) and neutrons (no charge). - Electrons (negatively-charged), surrounding the nucleus
Nuclide notation is a symbolic way to represent unique features of a particular atomic nucleus in the form . Isotopes Isotopes are atoms with same proton number but different nucleon number. E.g. Hydrogen isotopes are: ; Uranium are .
Nucleon number: total number of constituents in nucleus (protons + neutrons) Nucleons: constituents of nucleus (A nucleon can be either proton or neutron) Proton number: the number of protons in an atomic nucleus Protons are responsible for the nucleus to be positively-charged. It exists, with the same number of electrons, in the nucleus. Isotopes have same chemical properties as they have same number of electrons which are the particles involved in chemical reactions. 27.3 Nuclear Energy Let E = the energy (J) m = the mass (kg) c = speed of light (m/s) E = mc2 which means that energy is directly proportional to mass. A change in energy will therefore lead to corresponding change in mass. Nuclide Notation Let X = the element Y = nucleon number Z = atomic number Then an atom of an element is represented symbolically as: For example, the helium atom on Fig. 27.3 is represented by
where Δm = change in mass ΔE = change in energy Example What is the increase of mass when 4200J heat energy is absorbed by 1 kg of water to cause an increase of 1 K of temperature?
43 Mass of product particles is lower than reactant. WHY? Energy is directly proportional to mass (Einstein‟s law), therefore the more energy released, the more mass is lost. = 4.7 x 10-14 kg
Nuclear Fission It is the process where heavy, unstable nucleus breaks up to produce energy. This process is carried on in nuclear reactor to generate energy. HOW NUCLEAR REACTORS MAKE ENERGY FROM URANIUM
The isotope uranium-235 is bombarded by neutrons to form Uranium-236: + Uranium-236 is unstable and breaks down, splitting into 2 nearly equal radioactive nuclei, usually barium-141 and krypton-92, with production of 3 neutrons and energy, accompanied with increase in temperature: + +3 + energy Each neutron produced creates further fission by colliding with uranium-235 to form uranium-236 which again undergoes the fission and generates more fission fragments (products of fission), neutrons and energy, setting up chain reaction leading to extreme energy release and heat for generating power.
The product (fission fragments) increases in temperature. WHY? The 2 fission fragments, i.e. Barium-141 and Krypton-92, gain kinetic energy from energy released thus move faster and collide with surrounding atoms effectively, raising their kinetic energy leading to heat produced. Nuclear Fusion It is the process where lighter nuclides fuse together to form heavier nucleus with the release of energy. The energy released is due to loss of mass which is given by total mass of lighter nuclides minus mass of heavier nucleus formed. The temperature needed to start is about 100 million degrees Celsius. The Sun produces energy by fusion of hydrogen isotopes. Fusion Fission Fragments of explosion are Cause of energy Reduction in mass when light much lower than original nuclei is fused. to be created? nucleus. Break-up of heavy unstable Two light nuclei fuse to form nucleus by bombardment with single nucleus by raising neutrons; Chain reaction temperature; nuclei are Process enables process to carry on as brought together at high fission produces enough speed to overcome repulsion. neutrons to cause more fission. Easy to control. Rate of reaction Difficult to control Table 27.1 Summary of differences between fission and fusion 27.4 Nuclear Reactions An unstable parent nuclide X will disintegrate to a more stable daughter nuclide A with emission of α-particles, β-particles or γ-rays.
1. α-decay In α-decay, the parent nuclide has atomic number Z decreased by 2 and nucleon number Y decreased by 4 to form daughter nuclide . In general, the equation is: + + energy Parent nuclide Daughter nuclide + Helium (α-particles) + energy Example: + + energy Radium parent nuclide Radon daughter nuclide + α-particles + energy 2. β-decay In β-decay, the parent nuclide has atomic number Z increased by 1 and nucleon number Y unchanged to form daughter nuclide . In general, the equation is: + + energy Parent nuclide Daughter nuclide + Electron (β-particles) + energy Example: + + energy Sodium parent nuclide Magnesium daughter nuclide + β-particles + energy 3. γ-decay A parent nuclide is in excited state (having more amount of energy than it usually has) and will emit γ-rays due to its spare energy released and its daughter nuclide isotope unchanged. In general, the equation is: ( )* + γ-rays Excited parent nuclide Daughter nuclide + Gamma rays
Radioisotope Artificial radioactive isotope can be made by bombarding lighter molecules with protons, neutrons or α-particles. An example is nuclear power plants. END OF PURE PHYSICS SYLLABUS