4437 Revision Summary IGCSE Physics

IGCSE 44437 Double Award Science: Physics 1.2

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Understand and use distance-time graphs A horizontal (flat) line means that the distance is not changing with time. In other words, it is not moving.

By definition, speed = distance / time so the steepness (or gradient) of the line will give us the speed! Yellow: speed = distance / time = 30 m / 10 s = 3 m/s Blue: speed = distance / time = 20 m / 20 s = 1 m/s

P1.3

P1.4

P1.5

Interpret velocity-time graphs Always read the labels as the graph looks similar to a distance-time graph. Read “as the time increases, the speed does not change” This graph means that the speed is not changing!

As the time increases, the speed increases. This graph shows acceleration.

P1.6

IGCSE 44437 Double Award Science: Physics

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Shaded rectangle = 20 × 10 = 200 m White triangle = (20 × 20) / 2 = 200 m Total distance = 200 + 200 = 400 m

P1.7 P1.8

Express a force as a push or pull of one body on another Identify various types of force Gravitational- attractive force that pulls objects with mass Electrostatic- force that acts of 2 (or more) charged objects Opposite charges attract (positive-negative), like charges repel (positive-positive, negative-negative) Weight acts on a body close to earth P1.9 Friction is a force that acts in the opposite direction to motion Air resistance acts on bodies moving through air Water resistance acts on bodies moving through water Reaction acts on bodies touching a surface Tension acts on stretched objects, like stretched springs P1.10 (unbalanced) Force = mass x acceleration F=mxa P1.11 Weight = mass x ‘gravity’ W=mxg P1.12 Forces acting on a falling body Weight always acting down (never changes while the object is falling) Air resistance always acting up (in opposite direction to direction of movement) Air resistance increases as object gets faster Object accelerates as air resistance is smaller than weight Acceleration  speed increases  air resistance increases Terminal velocity when speed has increased so air resistance now matches weight

IGCSE 44437 Double Award Science: Physics

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P1.13 Stopping The time taken to stop something is called the stopping time. This is made up from the thinking and braking times. Thinking You must first decide whether to stop - the process of thinking takes time. We often call it the reaction time. Braking When the brakes are applied, the car slows down (decelerates). This also takes time: we call it the braking time. Stopping times are not actually that useful to us - we are normally more concerned about the stopping distance. Just as with times, the stopping distance is the total of two parts: Thinking Distance Whilst you are reacting to the hazard, the car is still moving! During your thinking time, you are not slowing down. We call the distance moved during this time the thinking distance. Factor Result Tiredness

Your brain thinks slower - you will not be able to apply the brakes as quickly.

Alcohol

Being under the influence - even legally - seriously alters how well you can judge hazards. Your body also moves less accurately. Late or missed braking results!

Drugs

Most drugs make you less alert and less aware of hazards. Even legal pain-killers and hay-fever tablets can seriously affect reaction times.

Distractions

In-car distractions (e.g. very loud music, mobile phones, crying babies, etc.) take your mind off the road ahead.

Braking Distance With the brakes applied, the car slows down. The distance that the car moves whilst braking is called the braking distance. Factor Result Brakes

Worn brakes won't work as well, so you'll need to brake for longer. Modern brakes are also better than old ones - they can apply bigger forces without causing skidding.

Tyres

Not all tyres are the same! Some are designed to reduce fuel consumption by rolling more easily. This is at the expense of grip in the wet. Tread patterns are designed to push water out from between the tyre and road. Good tyres can reduce braking distance by many metres! Worn tyres (with little tread) will have good grip in the dry but in the wet will lead to much longer braking distances...

Different types of surface provide different levels of grip, especially in the wet. If the road is wet, braking distance will always be longer. Oil Road Surface spills on the road, gravel, etc. all reduce grip and increase braking distances. Mass

The larger the total mass of the vehicle, passengers and luggage, the more kinetic energy it will have at a given speed. This increases the braking distance as it is harder to slow down.

Rather oddly, the worse your car's aerodynamics, the better it will be at slowing down during braking! The reason is that the airflow at and Aerodynamics around the car (drag or air resistance) is an additional force acting to slow you.

IGCSE 44437 Double Award Science: Physics

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P1.14

P1.15 See the document I’ve sent you on finding the centre of mass of a thin card On diagrams always draw the weight arrow through the centre of gravity P1.16 Helical springs obey Hooke’s Law over a large range of extensions Metal wires obey Hooke’s Law Rubber bands do not obey Hooke’s Law at large extensions P1.17 The straight part of a force – extension graph obeys Hooke’s Law. When the graph begins to bend, Hooke’s Law is broken.

IGCSE 44437 Double Award Science: Physics P2.2 P2.3

P2.4

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Common electrical conductors Common electrical insulators Metals Plastic water Air Hazards of electricity Long cables- trip hazard Frayed cables- electrocution Damaged plugs – electrocution Water around sockets/wet hands – Metal objects into sockets- electrocution electrocution Insulation. (a) Cables have a flexible plastic outer sleeve and the wires inside also have their own flexible plastic sleeves. These sleeves act as insulation layers which stop the copper core of the live wire from contacting the other wires, any metal part, or the skin of anybody that is touches the wire. (b) Plug casings are made of plastic or rubber. Molded plugs attached at the factory are molded to the cable and are even safer than the plugs that you can take apart. (c) Double insulation refers to an appliance that not only has insulated wires inside, but also has a casing made of plastic, so the potential live parts can't be touched.

P2.5 P2.6 P2.7

Earthing. Appliances with metal cases or other metal parts that might easily be touched are earthed. This means that there will be an earth wire connecting the metal case to the ground outside via the same electric cables that contain the live and neutral wires. Were the metal case to become live due to, for example, a loose live wire in contact with it, the current will flow directly to earth via the earth wire rather than via the person who is touching the casing, because the wire has much lower resistance that the human body and so takes virtually all the current. The earth wire in this situation acts as a short-circuit. Fuses and circuit beakers The main job of fuses and circuit breakers is to prevent electrical fires. (a) Fuses consist of an outer cartridge containing a fine wire. They are 'weak points' deliberately inserted into an electrical circuit. They get hot and melt if the current gets too big: the fuse is said to blow. Fuses are placed at the live side of appliances and they blow when there is a sudden big current flowing to earth. (b) Miniature circuit breakers do the same job as fuses. They are easier to use but costlier than fuses. They trip (i.e. the contacts separate) when there is too much current and can be easily reset by pressing a button on the outside of the circuit breaker. When a fuse melts or a circuit breaker trips, the circuit is broken and the current stops. A Residual Current Device (RCD) is a very sensitive type of circuit breaker. It trips on much lower currents than do ordinary circuit breakers and so act as an extra safety device if you are using an outside appliance such as an electric lawnmower, hedge trimmer or chain saw. (When you're standing on the grass, current due to an electrical fault will pass through you to the damp ground more easily than if you were inside standing on carpet floorboards, since earth is a better conductor.) Electrical heating is used in a wide variety of domestic contexts (in the home). Kettles, heaters, hair-driers, toasters etc. Current in a resistor transfers electrical energy to heat energy. When a resistor gains heat energy its temperature increases. (It gets hot!) Power = current x voltage P=IxV Choosing a fuse Calculate current (I = P / V)

IGCSE 44437 Double Award Science: Physics

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Choose a fuse that can carry a slightly higher current. Too high and it will not blow safely. Energy = Voltage x current x time NB Time MUST BE IN SECONDS! E= V x I x t P2.9 Mains electricity is A.C. Electricity from a cell/battery is D.C. Current/Voltage changes direction 50 times The current always flows from positive to every second. negative. P2.10 Parallel circuits are better in the home as they allow many different appliances to work independently at the same time. If one appliance broke in a series circuit, the whole circuit would be broken. Also, each parallel branch of the circuit will get 240V. Each part of a series circuit only gets a share of the full voltage, e.g. two bulbs in series would each get only (240V/2 =) 120V each so they would be dimmer. P2.11 The current in a circuit depends on the resistance of the component parts of the circuit and the applied voltage of the power supply. A circuit (with the same applied voltage) with more resistance will have less current flowing through it. P2.12 Current – Voltage graphs! P2.8

P2.13 If you increase the resistance of a circuit, the current in the circuit will decrease. If you decrease the resistance of a circuit, the current in the circuit will increase. P2.14 The resistance of a thermistor decreases as The resistance of an LDR decreases as the temperature increases. the light intensity increases.

2.15 2.16 2.17 2.18

Voltage = current x resistance V=IxR Current is the rate of flow of charge (Q). I = Q/t Charge = current x time Q=Ixt Current in a solid metallic conductor is a flow of negatively charged electrons.

IGCSE 44437 Double Award Science: Physics

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P2.19 A magnetic field line is also known as a line of force, showing the presence of a magnetic field. Magnetic field lines start on N poles and end on S poles. P2.20 An electric current produces a magnetic field around it. The Right hand grip rule. The thumb points in the direction of the current (positive to negative). The fingers of the right hand curl around the wire. The fingers point in the direction of the magnetic field (North  South).

P2.21 When a current-carrying wire is in a magnetic field, the magnetic fields interact, to attract or repel, just like permanent bar magnets. When the current changes direction (in a loudspeaker) the magnets are attracted and repelled, pushing the speaker cone in/out, making vibrations that are heard as sound. In an electric motor the forces are opposite on each side of the coil, causing the coil to rotate. P2.22 Fleming’s Left Hand Rule 1. Label current (all the way ‘round the circuit. 2. Label magnetic field in diagram (N  S) 3. Use the left hand rule to predict the direction of the force.

P2.23 The force gets bigger when

current is bigger magnetic field is stronger P2.24 When a conductor moves through a OR a magnetic field changes inside a magnetic field conducting coil Voltage is induced in the conductor (coil) The induced voltage increases when The speed of the conductor is higher The change in magnetic field is greater P2.25 Electricity is generated when Magnet rotates inside a coil of wire OR coil of wire rotates inside a magnetic field More voltage when magnet or coil rotate faster

IGCSE 44437 Double Award Science: Physics P3.2 P3.3

P3.4 P3.5 P3.6 P3.7 P3.8 P3.9 P3.10

P3.11

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Longitudinal waves Sound, earthquakes, ultrasound Transverse waves Water waves, light, EM radiation, waves on ropes Amplitude (A) is the maximum displacement of the particles in a wave Frequency (f) is the number of complete waves in 1 second Wavelength (λ)is the length of one complete wave Period (T) is the time for once complete wave Waves transfer energy/information without transferring matter. Wavespeed = frequency x wavelength V=fxλ Frequency = 1 / Period f = 1/ T You must be able to use P3.5 and P3.6 when dealing with waves including sound waves and light waves. Take care with units! The speed of sound is approx 330 m/s in air. Light is part of the electromagnetic (EM) spectrum All parts of the EM spectrum travel at the speed of light and behave like light. Recall the order of the EM spectrum including visible light (ROYGBIV) In decreasing wavelength and increasing frequency Radio  Microwave  Infra-red  ROYGBIV  Ultraviolet  X-rays  Gamma rays

IGCSE 44437 Double Award Science: Physics

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P3.12 P3.13 P3.14

Light waves are transverse waves. They can be reflected and refracted. Angle of incidence = angle of reflection (in a flat mirror) NB NORMAL line! Virtual image in plane (flat) mirror. Virtual image is ‘behind’ the mirror. It is not real. The virtual image (reflection) is the same distance from the back of the mirror as the object is away from the mirror. The image appear to be back to front.

P3.15 P3.16

Experiments to investigate the refraction of light in glass blocks/prisms. The refractive index n must be greater than 1, e.g. for water n is approx 1.33.

P3.17 P3.18

As with P3.15. Total internal reflection keeps light signals inside fibre optic cables, allowing large amounts of information to be transmitted quickly over great distances. Critical angle is the angle of incidence causing the angle of refraction to be 90 degrees. Remember n must be greater than 1! This means c must be less than 90 degrees e.g. for glass with n = 1.5, c is 41.8 degrees. Sound waves are longitudinal waves that can be reflected Humans can hear sounds in the range of frequencies from 20 Hz to 20,000 Hz (20 kHz) Measuring the speed of sound by simple direct method Stand 50 metres from a large smooth brick wall Clap once, (start stopwatch) wait to hear echo, then clap again 9 times. Stop stopwatch when you hear 10th (final) echo. Distance travelled by sound 50m x 2 (reflection) x 10 (claps) = 1000m. Speed of sound = distance / time. Speed of sound approx 330 m/s.

P3.19 P3.20 P3.21 P3.22 P3.23

IGCSE 44437 Double Award Science: Physics P4.2 P4.3 P4.4, P4.5 P4.6 P4.7 P4.8 P4.9, P4.10 P4.11 P4.12

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Energy transfers examples Energy cannot be created or destroyed. Efficiency must always be less than 1 (100%). The energy not converted to useful forms is usually converted to heat/sound due to friction. Heat (thermal) energy can be transferred by conduction (in solids), convection (in liquids or gases), or radiation (through a vacuum) Convection in everyday phenomena Fridges cooling elements are at the top of the fridge to cool the warm air that rises Kettles use convection to heat all of the water to an even temperature Insulation used to reduce (heat) energy transfers Curtains, carpets, draught excluders, loft insulation Cavity blocks, string vests, hair on arms/legs trap air Work done = Force x distance W=Fxd Work done = energy transferred Take care not to forget to square the speed when you calculate the energy.

P4.13

Conservation of energy means that you can assume that all energy is usefully converted from kinetic energy  potential energy  work. Of course all of it will not be usefully converted, so you can mention energy losses like heat/sound. P4.14, Power is measured in Watts (W) or P4.15 Joules/second (J/s). 1 kiloWatt (1kW) = 1,000 Watts.

P4.16

Almost all energy resources produce electricity by turning a turbine/generator.

Fossil fuels are burned to heat water to turn a turbine.

IGCSE 44437 Double Award Science: Physics

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P5.2

P5.3

Be able to describe how to determine the density of an irregular solid using a balance and displacement (Eureka) can.

P5.4

P5.5 P5.6

P5.7 P5.8 P5.9

P5.10 P5.11 P5.12

Pressure at any point in a liquid or gas acts equally in all directions Brownian motion describes the erratic and irregular motion of particles, such as pollen grains in water. Brownian motion happens when particles that are free to move around collide with each other, making them both bounce off in different directions. Many of these collisions occur to create the random paths that the particles take. As an example, observe the movements of pollen grains in water. If viewed under a microscope, you will see that they move around in completely random and erratic paths. What is happening is that the much smaller, and more numerous, water molecules are constantly bombarding them from all sides. More water molecules hitting the grain on one side than any other side produces a resultant force and the grain is pushed in that direction. This happens many times so that the grain follows a random path. Molecules of gas in a container move at random and collide with the container walls. They exert a force on the walls. The force acting over the area of the container walls results in pressure. Absolute zero is the lowest possible temperature and is equivalent to –273 degrees C The Kelvin temperature scale begins at absolute zero 0 K (zero Kelvin) = -273 degrees C. To convert Celcius to Kelvin add 273, e.g. 50 deg C = (50 + 273) 323 K NB Do this for every question about gases! Increasing the temperature of a gas will increase the speed of the molecules in the gas (temperature is related to energy) In a sealed container, pressure is proportional to Kelvin temperature For a fixed mass of gas at constant temperature p1 x V1= p2 x V2 (Boyle’s Law)

IGCSE 44437 Double Award Science: Physics P6.2 P6.3

P6.4 P6.5

P6.6 P6.7 P6.8 P6.9 P6.10 P6.11 P6.12 P6.13 P6.14

P6.15 P6.16

P6.17 P6.18 P6.19 P6.20

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Describe what is in an atom eg carbon-12 Oxygen-15 has 8 protons, (15-8)=7 atom has 6 protons, (12-6)=6 neutrons and neutrons and 8 electrons 6 electrons Atomic (proton) number is the number of Mass (nucleon) number is the number of protons(!) eg carbon 6 protons AND neutrons eg carbon-12 is 12 Isotope is an atom of the same element with different number of neutrons, e.g. carbon-12 (6 protons, 6 neutrons) and carbon-13 (6 protons, 7 neutrons) Alpha, beta and gamma radiations come out of unstable atomic nuclei. It is a random process. The radiations are ionising, i.e. they can form ions in the material they travel in. Alpha particles are made of 2 protons and 2 neutrons. Weak penetration. Beta particles are high-speed electrons. Gamma rays are high energy EM radiation. Strongest penetration. They can be distinguished (told apart) by their penetrating power. Alpha emission, mass number falls by 4, atomic number falls by 2. Beta emission, mass number does not change, atomic number increases by 1. Gamma emission, numbers do not change. Writing balanced nuclear equations. Make sure you know the numbers for each type of radiation. Treat each line as a maths equation. Ionising radiations can be detected by the effect they make on photographic film or in a Geiger-Muller tube. Background radiation sources; rocks, building materials, cosmic rays, nuclear weapons tests, food. Activity is the number of particles that are emitted from a radioactive source. It is measured in becquerel (Bq). The activity of a source decreases over time. Half-life is the average time taken for the activity of a sample to decrease to 50% of its original value. Each isotope has a different half-life. Calculations of half-life. Take care to check your answer! Radio(active)-isotopes are used to trace (follow) items or in medicine to trace the path of chemical in the body. It is also used in radiotherapy to treat cancers and to date archaeological specimens and rocks. Ionising radiations can cause mutations (cancer) in living organisms Radiation can damage living cells (tissue) Radioactive waste may be active for a very long time and have long-term effects on the environment. Geiger-Marsden (Rutherford) alpha-scattering experiment using gold foil Most of the alpha particles passed through the gold foil Some alphas were deflected, some (very few) alphas bounced back off the foil Rutherford’s model of the atom is a very small dense positive nucleus at the centre of an almost empty atoms, with electrons orbiting the nucleus Alphas passing straight through Atom is mostly empty space Alphas being deflected charged nucleus very small Alpha bouncing back Positively charged very dense nucleus Uranium-235 (U-235) can be split by fission when hit by a neutron The process releases energy as kinetic energy of the fission products U-235 induced fission produces 2 (large) daughter nuclei (usually Barium and Krypton) and a small number (2 or 3) neutrons A chain reaction can be started if neutrons produced by the first fission strike other U-235 nuclei In a nuclear reactor Control rods can absorb and stop the neutrons from causing further fission Moderator slows down neutrons so they can be absorbed by U-235