Additional Science P2 Edexcel GCSE Revision

TOPIC 1
1. STATIC ELECTRICITY
  1. Atoms have a nucleus containing protons and neutrons. Electrons move around the nucleus of an atom. An atom has the same number of protons and electrons, so the + and - charges balance and the atom has no overall charge.
  2. Insulating materials can be given an electrostatic charge by rubbing two materials together. Electrons are transferred from one material to another. The material that has gained electrons has a negative charge. The material that has lost electrons has a positive charge equal in size to the negative charge.
  3. A charged object (such as a plastic comb) can attract uncharged objects (such as small pieces of paper). This happens because the comb induces a charge in the pieces of paper.
2. USES AND DANGERS
  1. If you feel a shock by becoming in contact with an object, electrons are moving to "cancel out" the charge on you. This is called earthing. Lightning happens when a charge of static electricity builds up in clouds. When the charge is big enough, charged particles can flow through the air. The energy released by this causes light and sound. Lightning can kill living things and damage buildings.
  2. INSECTICIDE SPRAYERS - nozzle of the sprayer is connected to the electricity supply. Then the droplets all get a static charge. Then the droplets repel each other so the spray spreads out evenly.
  3. PAINT SPRAYING - the nozzle of the paint sprayer is connected to the electricity supply. Then the droplets get a static charge so they spread out evenly. Then the object being painted is given the opposite charge to the paint. The paint is attracted to the object being painted and less paint is wasted.
  4. Static electricity can build up on a plane as it flies. When it is being refuelled, the static charge may cause a spark when the nozzle of a fuel tanker touches the plane. This could cause an explosion if it ignited fuel vapour. A conducting wire called a bonding line is used to earth any static charge on the plan before refuelling starts. Electrons can flow along the wire to earth to neutralise the static charge on the plane.
3. ELECTRIC CURRENTS
  1. An electric current in a wire is a flow of electrons. The current supplied by cells and batteries is direct current.
  2. The size of a current is a measure of how much charge flows past a point each second. It is the rate of flow of charged particles. CHARGE = CURRENT X TIME
4. CURRENT AND VOLTAGE
  1. The current in an electric circuit is measured using an ammeter. The ammeter is placed in a circuit in series with the other components. The voltage is measured using a voltmeter. The voltmeter is placed in parallel with the component.
  2. The current in a series circuit is the same. A parallel circuit has more than one path for current to flow through. The current splits up when it reaches a junction and comes back together when the wires re-join.
5. RESISTANCE, CURRENT AND VOLTAGE
  1. The resistance of a component is a way of measuring how hard it is for electricity to flow through it. The higher the resistance, the smaller the current. The resistance of a circuit can be changed by putting different resistors into the circuit.
6. CHANGING RESISTANCES
  1. FILAMENT LAMPS - get hotter as the voltage increases. This increases their resistance. The higher the temperature, the higher the resistance.
  2. DIODES - when the current flows in one direction, diodes behave like fixed resistors. The resistance does not change if the voltage changes. Diodes only conduct electricity in one direction.
  3. LIGHT-DEPENDENT RESISTORS - the resistances of these is large in the dark. The resistance gets less if light shines on it. The brighter the light, the lower the resistance.
  4. THERMISTORS - the resistance of these depends on its temperature. The higher the temperature, the lower the resistance.
7. TRANSFERRING ENERGY
  1. Energy is transferred to a resistor when a current flows through it. The energy transfer heats the resistor. The heating effect is useful in electric fires/cookers.
  2. The POWER of an appliance is the energy transferred per second. Electrical power = current x potential difference
  3. The total ENERGY transferred by an appliance depends on its power and how long it is switched on for. Energy transferred = current x potential difference x time
TOPIC 2
1. VECTORS AND VELOCITY
  1. Some quantities are vectors. They have a direction as well as size. Vectors include displacement, velocity, force and acceleration.
  2. A distance - time graph shows us a particular journey. The line sloping shows that they are moving. The horizontal line shows that they are stationary. Speed = distance/time.
2. VELOCITY AND ACCELERATION
  1. Acceleration is a change in velocity and its a vector quantity. Acceleration = change in velocity/time taken
  2. This velocity-time graph shows how the velocity of a train along a straight track changes with time. When the velocity is at 0, the train is stationary. The sloping line shows that the train is accelerating.
3. RESULTANT FORCES
  1. A force is a vector quantity, because it has a direction as well as a size. A free-body force diagram represents all the forces on a single body. Larger forces are shown using longer arrows.
  2. ACTION REACTION FORCES - two touching objects exert forces on each other, e.g. the force from the foot on the ball is the action force. The ball exerts an equal opposite reaction force on the boot.
4. FORCES AND ACCELERATION
  1. The acceleration produced by a resultant force depends on the size of the force and the mass of the object. The greater the force, the greater the acceleration. The greater the mass, the smaller the acceleration. Force = mass x acceleration.
5. TERMINAL VELOCITY
  1. Mass is the amount of matter in an object, and is measured in kg. Weight is the force of gravity on an object and is measured in Newtons. On Earth, every kg of mass is pulled down with a force of 10N. Weight = mass x gravitational field strength.
  2. The force of gravity on a large mass is greater than on a small mass, but the large mass also needs a greater force to accelerate it.
6. STOPPING DISTANCES
  1. Thinking distance + braking distance --> stopping distance.
  2. Factors that affect stopping distance = mass of vehicle, speed, reaction time
7. MOMENTUM AND SAFETY
  1. The momentum of a moving object depends on its mass and its velocity. It is a vector quantity. Momentum = mass x velcoity
  2. When two objects collide, the total momentum before the collision is the same as the total momentum after the collision. Momentum is conserved.
  3. Bubble wrap is used to protect fragile items. if something hits the wrapped object the air in the bubbles squashes and reduces the force on the object,
  4. Seat belts stretch and slow you down gradually. When you slow down gradually, the rate of momentum is less and so there are smaller forces on you, and you are less likely to crash.
8. WORK AND POWER
  1. Work is the amount of energy transferred. Work = force x distance. Power is the rate of doing work. Power = work done/time taken.
9. POTENTIAL AND KINETIC ENERGY
  1. Gravitational potential energy is the energy stored in an object because it is in a high position. Gravitational potential energy = mass x 10N/kg x vertical height
  2. Kinetic energy is the energy stored in moving objects. Kinetic energy = 0.5 x mass x velocity squared
  3. CONSERVATION OF ENERGY - energy cannot be created or destroyed. It can only be transferred from one form to another.
10. BRAKING AND ENERGY CALCULATIONS
  1. A force is needed to make an object change speed. Force = change in momentum/time
TOPIC 3
1. ISOTOPES
  1. Atoms of a particular element always have the same number of protons, but different numbers of neutrons, are isotopes/
2. IONISING RADIATION
  1. Some elements are radioactive. Their nuclei is unstable: alpha particle is a helium nucleus and has an electrical charge. A beta particle is an electron, and has an electrical charge. Gamma radiation is a form of electromagnetic radiation.
  2. Alpha particles = very ionising. Can be stopped by paper. Beta particles = moderately ionising. Can be stopped by aluminium. Gamma rays = weakly ionising. Need thick lead to stop them.
3. NUCLEUR REACTIONS
  1. In a fission reaction, a large unstable nucleus splits into two smaller ones, e.g. uranium-235 nucleus splits up when it absorbs a neutron. The fission of uranium-235 produces 2 daughter nuclei, two or more neutrons, and releases energy.
  2. A chain reaction is when the neutrons released by the fission of U-235 are absorbed by other nuclei, and each of these nuclei undergo fission, and produce more neutrons. A chain reaction can be controlled by using a different material to absorb some of the neutrons. This slows the reaction as there are fewer neutrons.
4. NUCLEAR POWER
  1. Nuclear power stations use nuclear fuels such as uranium-235. The fuel is made into fuel rods. A reactor core is made of a material called a moderator. Fuel rods and control rods fit into holes in the moderator. The moderator and control rods help to control the chain reaction.
  2. The control rods absorb neutrons. If the control rods are pushed down the core, more neutrons are absorbed and the chain reaction slows down. The neutrons produced by fission reactions are moving fast. The moderator slows them down so they are more likely to be absorbed by another U-35 nucleus and cause another fission reaction.
  3. Thermal energy released by the chain reaction is used to turn water into steam. The steam makes a turbine spin, and the turbine drives a generator. The daughter nuclei produced in the fission reaction are radioactive. They neutrons passing through the core can produce other radioactive isotopes. This radioactive waste must be disposed of safely.
5. FUSION
  1. Nuclear fusion happens when small nuclei join to form larger ones. Fusion reactions release energy. Isotopes of hydrogen combine in the Sun to form helium. The energy released by these reactions makes the Sun shine.
  2. Nuclei need to get close to each other before fusion can happen. The high temperatures and pressures needed are difficult to produce is a fusion reaction.
6. NUCLEAR WASTE
  1. Three types of waste: high level waste, intermediate level waste and low level waste.
  2. Waste can be disposed of by firing it into space, and dumped at sea.
7. USES OF RADIATION
  1. We are always exposed to background radiation, e.g. radon is produced when uranium decays. Radon can be built up in houses and buildings.
  2. Radiation is used in hospitals to kill cancer cell, diagnose cancer and sterilize surgical instruments. Gamma rays make food safer to eat.
  3. Other uses of radiation are used to find leaks in pipes, to control thickness, and smoke alarms.

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