PHYSICS UNIT 2 Physics P2 for GCSE Additional Science or GCSE Physics

AQA GCSE Science PHYSICS 2 Unit P2.4 Using mains electricity safely and the power of electrical appliances

• Appreciate that mains electricity is useful but can be very dangerous and it is important to know how to use it safely.

• Know that electrical appliances transfer energy.

• Know and understand that the power of an electrical appliance is the rate at which it transforms energy.

• Know and understand that most appliances have their power and the potential difference of the supply they need printed on them.

  • Appreciate that from this information we can calculate their current and the fuse they need.

• You should be able to use your skills, knowledge and understanding to:

  • understand the principles of safe practice and recognise dangerous practice in the use of mains electricity,

  • compare the uses of fuses and circuit breakers,

  • evaluate and explain the need to use different cables for different appliances,

  • consider the factors involved when making a choice of electrical appliances eg

    • you should consider the efficiency and power of the appliance.

AQA GCSE Science PHYSICS Unit P2.4.1 Household electricity

• a) Know and understand that cells and batteries supply current that always passes in the same direction.

  • Know that this is called direct current (d.c.).

• b) Know and understand that an alternating current (a.c.) is one that is constantly changing direction.

  • You should be able to compare and calculate potential differences of d.c. supplies and the peak potential differences of a.c. supplies from diagrams of oscilloscope traces.

  • HT only: You should be able to determine the period and hence the frequency of a supply from diagrams of oscilloscope traces.

• c) Know and understand that mains electricity is an a.c. supply.

  • In the UK it has a frequency of 50 cycles per second (50 hertz) and is about 230 V.

• d) Know that most electrical appliances are connected to the mains using cable and a three-pin plug.

• e) Know the structure of electrical cable.

  • You should be familiar with both two-core and three-core cable.

• f) The structure and wiring of a three-pin plug.

  • Knowledge and understanding of the materials used in three-pin plugs is required, as is the colour coding of the covering of the three wires.

• g) Know and understand that if an electrical fault causes too great a current, the circuit is disconnected by a fuse or a circuit breaker in the live wire.

• h) Know and understand that when the current in a fuse wire exceeds the rating of the fuse it will melt, breaking the circuit.

• i) Know that some circuits are protected by Residual Current Circuit Breakers (RCCBs).

  • You should realise that RCCBs operate by detecting a difference in the current between the live and neutral wires.

  • Knowledge of how the devices do this is not required.

  • You should know that this device operates much faster than a fuse.

• j) Know and understand why, appliances with metal cases are usually earthed.

  • Know that some appliances are double insulated, and therefore have no earth wire connection.

• k) Know that the earth wire and fuse together protect the wiring of the circuit.

  • You should have an understanding of the link between cable thickness and fuse value.

AQA GCSE Science PHYSICS Unit P2.4.2 Current, charge and power

• a) Know that when an electrical charge flows through a resistor, the resistor gets hot.

  • You should understand that a lot of energy is wasted in filament bulbs by heating.

  • Know that less energy is wasted in power saving lamps such as Compact Fluorescent Lamps (CFLs).

  • You should understand that there is a choice when buying new appliances in how efficiently they transfer energy.

• b) The rate at which energy is transferred by an appliance is called the power.

  • Be able to use the equation:

  • power = energy transferred / time

  • P = E / t

  • P is power in watts, W

  • E is energy in joules, J

  • t is time in seconds, s

• c) Know that power, potential difference and current are related by the equation:

  • Be able to use the equation:

  • power = current x voltage (p.d. volts)

  • P = I x V

  • P is power in watts, W

  • I is current in amperes (amps), A

  • V is potential difference in volts, V

    • You should be able to calculate the current through an appliance from its power and the potential difference of the supply, and from this determine the size of fuse needed.

• d) HT only: Energy transferred, potential difference and charge are related by the equation:

  • HT only: Be able to use the equation:

  • energy transferred = voltage (p.d.) x charge

  • E = V x Q

  • E is energy in joules, J

  • V is potential difference in volts, V

  • Q is charge in coulombs, C

• Practical work in unit 2.4 to help develop your skills and understanding may have included the following:

  • measuring oscilloscope traces

  • demonstrating the action of fuse wires,

  • using fluctuations in light intensity measurements from filament bulbs to determine the frequency of a.c.,

  • measuring the power of 12 V appliances by measuring energy transferred (using a joulemeter or ammeter and voltmeter) in a set time.