Mr Palmer's AQA GCSE Physics Notes

Mains Electricity



UK Electrical Plug











The case is made of plastic because it is sturdy and a good insulator. It contains:

The pins which are the parts that plug into the wall socket. They are made from brass because it is a good conductor and is sturdy.

The fuse is used to protect the appliance/operator if the appliance draws too much current. The fuse is always connected to the live wire.

The blue wire is neutral. It's potential difference is zero compared to the earth.

The brown wire is live. It alternates between positive and negative potential compared to the neutral wire.

The yellow/green wire is earth.

(Mnemonic: The live brown cow stood on the green and yellow earth and looked up into the neutral blue sky)

The cable contains the three wires (neutral, live and earth) each made of copper and covered by a layer of plastic. Then all three are bound together with another layer of plastic.

Copper is used because it is flexible and a good conductor. Plastic is used because it is flexible and a good insulator.

UK household mains is supplied at 230 volts.



The Oscilloscope





  • f: the frequency of a wave measured in Hertz (Hz)

  • T: the period of a wave measured in seconds (s)





    • Electrical Safety



    If an electrical fault causes too great a current the circuit should be switched off by a fuse or circuit breaker.

    When the current in a fuse wire exceeds the rating of the fuse it will melt, breaking the circuit.



    Electrical Power





  • P: power of an electrical device measured in watts (W)

  • V: potential difference across the device measured in volts (V)

  • I: current through the device measured in amperes (A)



    • Remember: A watt is 1 joule per second and one kilowatt is 1,000 watts.









    Example:

    If the ammeter reads 2.5A and the voltmeter reads 1.6V, calculate the electrical power of the motor.











    We can also use the following formula for power as well:



  • E: energy transferred to an electrical device measured in joules (J)

  • P: power of the electrical device, measured in watts (W)

  • t: time measured in seconds (s)



    • The 4W motor is left on for one hour. What is the total energy transferred to the motor during that time?













    Electrical Energy





  • E: Energy transferred to an electrical device measured in joules (J)

  • V: potential difference across the device measured in volts (V)

  • Q: charge passing through the device measured in coulombs (C)





    • The Circuit Breaker








    A circuit breaker protects a circuit from drawing too much current. Unlike a fuse which melts and must be replaced, a circuit breaker can simply be reset when the problem in the circuit is solved. It works in the following way:

    1. When the current in the circuit gets too high it causes the electromagnet to turn on.

    2. The electromagnet pulls on the iron bolt with a force greater than the springs holding it up. The iron bolt slides down into the electromagnet.

    3. Without the iron bolt holding it in place, the plunger is now pushed back by its springs

    4. When the plunger is pushed back, it no longer makes contact with the circuit on the left. Thus no more current can flow, turning off the circuit

    5. When the reset button is pressed the plunger and iron bar slide back into their starting positions and the circuit can be used again





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    Physics P1 Topics
    1. Heat
    2. Energy
    3. Electricity
    4. Power
    5. Electromagnetic Spectrum
    6. Nuclear Radiation
    7. Origins of the Universe


    Physics P2 Topics
    1. Motion
    2. Forces
    3. Energy
    4. Static Electricity
    5. Current Electricity
    6. Mains Electricity
    7. Momentum
    8. Nuclear Physics

    Other
    1. Mathematics for Physics