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Physics IGCSE Revision
Volume and Density
Mass Density = Volume
m ρ(rho) = V
Volume and Density How to find the volume of an irregular solid? • You need to fill up a measuring cylinder with water and measure till where it is filled. • Then lower the irregular solid into the measuring cylinder and measure how much the water has risen. • Subtracting the two values that you have will give you the volume of the substance.
Speed Speed
=
Distance Time
Velocity
Average Acceleration
Negative acceleration is called deceleration or retardation
=
v-u a= t
Change in velocity Time Taken
v= final velocity u=initial velocity
Forces
• A force is a push or a pull. • Force is measure in Newton's (N). If no external forces are applied to an object: - It will remain stationary - It will keep moving at a constant speed. What is Terminal Velocity? It is when something is at its maximum speed.
Forces Force = Mass x Acceleration F
=
m x a
Friction
• Friction is a force that stops two materials from sliding across each other. • Static Friction resists the lateral (sideways) movement of two objects. • Dynamic Friction is the friction between two objects that are moving. It heats up the material. When something is moved against the force of friction the kinetic energy is changed into thermal energy. STATIC FRICTION IS GREATER THAN DYNAMIC FRICTION
Gravitational Force • All the masses attract each other. • The greater the mass, the greater the force. • The closer the mass, the greater the force. • To every action there is an equal but opposite reaction.
Gravitational Force
Weight = Mass x Gravity W =
m x g
The Parallelogram Rule
1. First you need to draw the two lines given to you. The directions should be accurate and the length of each line should be in proportion to the magnitude of each vector. 2. Then draw in two more lines to complete the parallelogram. 3. Diagonal from ‘O’ and then measure its length.
Centripetal Force • It is an inward force needed to make an object move in a circle. More centripetal force is needed if: - Mass of the object is increased - Speed of the object is increased - Radius of the circle is increased.
Moments Moment of a force about a point
= Force x Perpendicular distance from the pivot
The Principle of Moments Clockwise moments = Anticlockwise moments
Hooke’s Law A material obeys Hooke’s law if, beneath the elastic limit, the extension is proportional to the load.
Load =
F
Spring x Constant
=
k
Extension
x
Pressure Pressure =
Force Area
Pressure in Liquids • • • •
Its in all directions It increases with depth It depends on the density of the liquid It doesn’t depend on the shape of the container. Pressure = Density x Gravity x Height
pressure
= ρ(rho) x g x h
Hydraulic Jack* Output Force Input Force
=
Output Piston area Input Piston area
Pressure in Air • Pressure decreases as you rise through it. • It acts in all directions. Barometer: Measures atmospheric pressure Manometer: Measures the pressure difference
Gas Law • When studying a gas, the following things should be considered: a) Pressure b) Volume c) Temperature • Gas Law: For a fixed mass of gas the pressure times the volume divided by the temperature is constant
PxV = Constant T
Energy Work = Force Done
W =
x
F
Distance moved in the direction of the force
x d
Different Forms of Energy • • • • • • • • •
Kinetic energy Potential energy Gravitational energy Elastic energy Chemical energy Electrical energy Nuclear energy Thermal energy Radiated energy
Energy
• The law of conservation of energy Energy cannot be made or destroyed, but it can change from one form to another.
Gravitational potential energy Kinetic Energy
=m x gx h
=½ mv
Gain in kinetic energy is a loss in potential energy
2
V = Speed
Scalar and Vector Quantities Scalar: has magnitude but no direction -Speed (magnitude of velocity) - Time - Mass
Vector: has magnitude and direction. -Energy -Displacement -Velocity -Acceleration
Efficiency and Power
Efficiency =
Useful Work done
Total energy input
Work done Power = Time Taken Useful Power = Output
Force x
Speed
Thermal Power Stations Fuel burner Nuclear reactor
Electricity
Fuel
+
Oxygen
Thermal Energy
Boiler
Generator
Carbon Dioxide
Turbines
+
Water
+
Thermal Energy
Thermal Power Stations Problems • Increased rate of global warming • Sulphur dioxide causes acid rain • Transporting fuels could lead to pollution due to leaks • Radioactive wastes are very dangerous • Nuclear accidents
Power Schemes 1- Pumped storage scheme – wind farms 2- Tidal power scheme 3- Hydroelectric power scheme
Energy Sources Non-renewable
Coal, oil, natural gas - Supplies are limited - Carbon dioxide concentration is increasing Nuclear fuels - Expensive to build and decommission
Renewable Hydroelectric and tidal energy - Expensive to build - Few areas are suitable - May cause environmental damage Wind energy - Large, remote, windy sites required - Noisy, ruin landscape Wave energy - Difficult to build Geothermal energy - Deep drilling difficult and expensive Solar energy - Sunshine varies - Solar cells difficult to transport
Thermal Effects • Solids-fixed volume and shape • Liquids-fixed volume but no fixed shape • Gases-no fixed shape and no fixed volume. • Internal energy: total kinetic and potential energy of all atoms in a material. Objects as the same temperature have the same average kinetic energy per particle Hotter material faster the particles move the more internal energy it has
Absolute Zero -273˚C= 0 Kelvin (0 K) Kelvin Temperature/K = Celsius Temperature/˚C+273 This is the lowest temperature there is. It is a thermodynamic scale. It is based on the average kinetic energy of particles.
Thermal Effects • Thermal expansion: this is when a substance is heated and its volume slightly increases. The pressure law: - When the Kelvin pressure doubles so does the pressure - Pressure ÷ Kelvin temperature always has the same value Thermal Conduction: Conduction is the process by which thermal energy is transferred from the hot end to the cold end as the faster particles pass on their extra motion to particles along the bar.
Thermal Effects • More thermal energy is transferred if : - Temperature difference across the ends is increased. - Cross-sectional area of the bar is increased - Length of the bar is reduced.
Convection
Hot air rises and cold air sinks ☺
Thermal Radiation
• This is when things that absorb this radiation are warmed up. To increase the rate of evaporation - Increase the temperature - Increase the surface area - Reduce humidity - Blow air across the surface
Specific Heat Capacity Specific Temp Energy = mass x x heat change Transferred capacity Energy Transferred Specific heat capacity is 4200J/K kg for water
=m x c x∆t
Latent Heat of Fusion Energy Transferred
Specific Latent x = Mass
Energy Transferred
Heat
= mL
Describing Waves Amplitude
Wavelength
Transverse Waves
• The oscillations are at right angles to the direction of the wave. • For example light waves.
Longitudinal Wave ( Rarefactions)
• It consists of compressions and rarefactions. • Oscillations are in direction of travel. • For example: Sound waves.
The Wave Equation
Speed = Frequency x wavelength
V = = Lambda
f x
Wave Effects: Reflection
The waves are reflected from the surface at the same angle they hit it.
Wave Effects: Refraction Plastic
Due to the plastic the water becomes shallower causing the waves to slow down. This effect is called refraction.
Wave Effects: Diffraction
• Diffraction is when the light bends around obstacles. • Wider gaps produce less defraction.
Sound waves
• Sound waves are caused by vibration • Sound waves consist of Longitudinal waves. - Compression passes Air pressure increases -Rarefaction passes Air pressure decreases
Sound Waves • Sound waves need a medium to travel in. For instance the air. • Sound waves can also be diffracted due to their long wavelength. • They can be displayed on an oscilloscope. The sound enters via the microphone, a metal plate vibrates, these vibrations cause electrical oscillations producing a wave front. IT IS NOT A PICTURE OF THE SOUND WAVE BECAUSE SOUND WAVES ARE NOT TRANSVERSE
Speed of Sound • Temperature of air: Sound travels faster through hot air. • Does NOT depend on pressure: the pressure may change but the speed of the wave will remain the same • The speed of sound is different through different materials.
Ultrasound: sounds above the range of human hearing which is between 20Hz & 20kHz
How to Measure the speed of an echo?
To measure echo
Speed
=
Distance Time
Take note here the distance is the distance from to the wall and then BACK !
You could use: - Echo-sounder - Electronic tape measure (Works like an echosounder) - Radar
Features of Light 1. 2. 3. 4. 5. 6.
Form of radiation Travels in straight lines Transfers energy Transverse waves Can travel through vacuum 300,000 000 m/s
Law of reflection • i˚=r˚ • i, r and normal lie on the same plane.
Total Internal Reflection
• Anything greater than the critical angle does not have a refracted ray. Which means that all the light is reflected thus leading to TOTAL internal reflection.
Lenses Convex Lens
Convex lenses are used in projectors as they form large, inverted, real images on the screen
Concave Lens
When the object is less than F1
Refracted Object
Original Object
Refracted image is -Upright -Larger -Virtual -It is also on the same side as F1
When the object is at 2F
1
Refracted image is -At 2F2 -Inverted -The same size -Real
When the Object is between F1 and 2F1
Refracted image is -Beyond 2F -Inverted -Larger -Real
When the object is beyond 2F1
Refracted image is -Between F2 and 2F2 -Inverted -Smaller -Real
The Electromagnetic Spectrum
Electromagnetic waves are emitted when a charged particle oscillate or loose energy in some way.
Electricity • Rubbing materials does not MAKE charge, it only separates charges that are already there. • Induced charge: this is the charge that ‘appear’ on an uncharged object because of the charged object nearby. Charge is measured in Coulombs.
Electricity* • Electrostatic precipitators: are fitted into chimneys in order to reduce pollution
Electricity • When there are no ions in the air it is a good electrical insulator. • When there are ions present in the air it is a good conductor
Current is measured in amps.
Current • Current remains the same at all points round a simple circuit.
Charge = Current x Conventional Current flows from positive to negative. Electron flow is from negative to positive.
Time
Potential Difference (Voltage) • The highest potential difference is when it is not in a circuit and it not supplying current. This is also known as the Electromotive force. • In a simple circuit, the sum of the PD’s across the components is equal to the PD across the battery.
Resistance Resistance =
PD (Voltage)
R =
Current (A) V I
Ohms Law The current is proportional to the PD.
How can resistance be increased? 1- Length : Doubling the length increases resistance 2- Cross-sectional area: halving the surface area. (thin wire is more resistance than a thick one) 3- Material 4- Temperature: resistance increases with temperature
CIRCUITS -
Parallel Circuit Gets full PD from the battery One bulb removed the other still works Total current = Sum of the currents in the branches. Resistance:
-
Series Circuits Bulbs share PD One bulb removed, the other one goes out. Current through each component is the same Resistance:
CIRCUITS Parallel Circuit
Series Circuits
Power
Work done Power = Time taken
Power Power = Current x P
= Ix V
Voltage
Power Power = Current x Resistance 2
P
=I x R 2
Electrical Energy Equation Energy = PD x Current x Time Transformed E = V x I x t
Brief Intro on Magnets Magnetic material- is a type of material that can be magnetized and is attracted to other magnets. Strong metals contain 1- iron They are called 2- nickel “Ferromagnetics” 3- cobalt Iron and alloys of iron are
called ferrous. (Ferrous in Latin means iron) Aluminium, copper, and other non-magnets are called nonferrous.
Properties of magnets: • Have a magnetic field around them • Has two poles exerting forces on other magnets. – Like poles repel – Unlike poles attract
• Attract magnetic materials by inducing magnetism in them.
What is induced magnetism?
Some metals like iron and steel are attracted to other magnets because if there is a magnet near by, they themselves get magnetized. Magnetism is INDUCED in them. – When steel is pulled away from a magnet, it keeps its induced magnetism causing it to become a permanent magnet.(hard magnet) – When iron is pulled away from a magnet, it looses its induced magnetism meaning that iron was only a temporary magnet.(soft magnet)
Magnetic Effects of Current • When an electric current is passed through a wire an magnetic field is produced. The features of this magnetic field are: – They are circles – Field is strongest close to the wire – Increasing current increases strength of field.
Right-hand grip rule
Electromagnets
• These are types of magnets that can be switched on and off.
Iron core
The strength of the magnetic field can be increased by: - Increasing the current. - Increasing the number of turns in the coil
Coils
Magnetic Relay Metal contacts.
• When electricity is passed through the coil end wires, it induced a magnetic field in the iron ROD. This attracts the iron STRIP causing both metal contacts to touch.
Circuit Breaker
Circuit breaker- it is an automatic switch cutting off the current within a circuit if it rises above a specified value.
- In the case on the left, the pull of the electromagnet has become so strong that it has attracted the soft iron armature. This causes the contacts to open and stop the current. - If u press the reset button, the contacts close once again.
Magnetic force on the current • Copper is a nonmagnet feels no force of the magnet But.. • If it has a current passing through it, there will obviously be a force on the wire. The wire moves ACROSS the field. It is not attracted to it.
Force is increased if: -Current is increased -Stronger magnet is used -Length of wire in field is increased.
Flemings Left Hand Rule
Electric motors
An electric motor transfers electrical energy to kinetic energy.
• A motor is made up from a coil of wire which is positioned between the two poles of the magnet. • When the current flows through the coil, it creates a magnetic field. This magnetic field that is produced interacts with the magnetic field produced by the 2 permanent magnets. • The combination of these two magnetic fields exert a force, pushing the wire at right angles to the permanent magnetic field.
Improve turning effect
Increasing Turning Effect • • • •
Increase the current Use a stronger magnet Increase the number of turns on the coil Increase the area of the coil.
Electromagnetic Induction • A magnetic field can be used to produce current. When the wire is moved across the magnetic field a small EMF(voltage) is created. This is called electromagnetic induction. “EMF is induced” Induced EMF increased by: -Moving wire faster -Using stronger magnet -Increasing length of wire.
Induced Currents Fleming’s right hand rule:
Difference between the left hand and the right hand rule: -When current causes motion the left hand rule applies -When motion causes current the right hand rule applies
Generators • • • • •
The coil rotates Magnetic fields are cut EMF is generated Causes current to flow Coil rotates– upwards, downwards, upwards causing the current to flow backwards, forwards, backwards.
Increasing EMF: - Increasing the number of turns on coil - Increasing area of coil - Use stronger magnet - Rotate coil faster
Coils and Transformers • Moving magnet induces EMF • Magnetic field SAME effect. • Mutual induction: when coils are magnetically linked so that changing current in one coil causes an induced EMF in the other.
Simple Transformer
output voltage Input voltage
=
Turns in output coil Turns on input coil
- Alternating current flows through primary coil - This sets up an altering magnetic field in the core. - Coils of the secondary coil ‘cut’ the altering magnetic field thus inducing an alternating voltage in the output coil.
Step-up and Step-down transformers Step-up: this is when the number of output coils is greater than the number of input coils which means that there will be a greater output voltage as opposed to input voltage. Step-down: this is when the number of output coils is less than the number of input coils which means that there will be less output voltage as opposed to input voltage.
Power Through a Transformer Input x Input = Output x Output voltage current voltage current
Generator (Electric Motor): Current + Magnetic Field = Motion Electromagnetic Induction: Magnetic Field + Motion = Current
Thermionic Emission
• Basically what happens in thermionic emission is that the tungsten filament is heated to 2000 degrees Celsius. Some electrons that are hot enough escape the surface of the white hot surface. These then pass through the vacuum and on the screen.
The Oscilloscope
• The Cathode Ray Oscilloscope uses (as mentioned on previous slide) an electron gun and the X and Y plates to adjust where the stream of electrons go. • The X-Plates move the beam horizontally (Left or Right) • The Y-Plates move the beam vertically (Up or Down)
• The Y-plates are connected to a Y input terminal. These are connected to an AC supply. Examples of things that use electron beams: - Television - X-ray tube
Atoms
Nuclear Radiation
Alpha Alpha particles are made of 2 protons and 2 neutrons. This means that they have a charge of +2, and a mass of 4. Alpha particles are relatively slow and heavy. They have a low penetrating power - you can stop them with just a sheet of paper. Because they have a large charge, alpha particles ionize other atoms strongly
Beta •Beta particles have a charge of minus 1, and a mass of about 1/2000th of a proton. . •They are fast, and light. •Beta particles have a medium penetrating power - they are stopped by a sheet of aluminum •Beta particles ionize atoms that they pass, but not as strongly as alpha particles do.
Gamma •Gamma rays are waves, not particles. This means that they have no mass and no charge. •Gamma rays have a high penetrating power it takes a thick sheet of metal such as lead, or concrete to reduce them significantly. •Gamma rays do not directly ionize other atoms •We don't find pure gamma sources - gamma rays are emitted alongside alpha or beta particles. Strictly speaking, gamma emission isn't 'radioactive decay' because it doesn't change the state of the nucleus, it just carries away some energy.
In a Magnetic Field
What is Background Radiation? • Background radiation comes from naturally decaying substances such as soil, rocks, air, food and drink. • It is detected by a Geiger Muller Tube
Radioactive decay- Alpha Decay
Radioactive decay- Beta Decay
Half-Life
• This is the amount of time taken for the nuclei of a radioactive substance to decay.
Nuclear Fusion
This does not take place on Earth so far. It is the process that powers the stars.
Nuclear Fission
What can Radioactivity be used for? 1. 2. 3. 4. 5.
Tracers Radiotherapy Testing for cracks Thickness monitoring Carbon Dating- after an organism dies the amount of C-14 inside it begins to decay. It can be used to find out how old a substance is. 6. Dating Rocks
This is the physics syllabus Complete
Best of luck for your IGCSE exams IMPORTANT: Come to school during study leave and ask your questions
EXTRA NOT IN SYLLABUS
Important electronic components 1. Resistors – keep currents + voltages at levels desired by the electronic component 2. Capacitor – store small amounts of electric charge 3. Diodes – allow the current to flow in only one direction 4. Light-emittingg diodes (LED) – glow when a small current is passed through them.
Continued… 5. Transistors – used to amplify signals 6. Integrated circuits(micro-chips)– contain complete circuits with : a) Resistors b) Transistors c) Other components
7. Relays– electromagnetic switches.
Diodes • Can be used to change AC to DC Rectification • Lets forward parts of the AC through but blocks the backwards part. • Forming a DC Input
1 resister
Output
Potential Divider • A potential divider only delivers a portion of the voltage.
Reed Switch • A reed switch is operated by a magnetic field.
Transistors as switches • It is a semiconductor device made of silicon.
Collector
Base
Emitter
The NPN resistor 1000 ohms
b
6V
c
e
• 1. 2. 3. 4.
In the diagram above there are actually two circuits put together as one. The first circuit is the one with the base and the emitter ( input circuit) and the second is the circuit with the collector and the emitter (output circuit). Two input connections joined together no current flow Input the base greater than 0.6Vlamp switches on 1000 ohm resister is present to protect the input to the resistor, allowing input to be higher than 0.6V to 5V without harming transistor. Little current is needed in the input circuit.
Logic Gates
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