P 2 Physics Mains Electricity P 2 Physics

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P 2 - Physics Mains Electricity

P 2 - Physics Mains Electricity

P 2 – Physics - Aims � to recognise errors in the wiring of

P 2 – Physics - Aims � to recognise errors in the wiring of a three-pin plug � to recognise dangerous practice in the use of mains electricity � to compare potential differences of d. c. supplies and the peak potential difference of a. c. supplies from diagrams of oscilloscope traces � (HIGHER ONLY) to determine the period and hence the frequency of a supply from diagrams of oscilloscope traces

P 2 – Physics – Mains Electricity Mains electricity is useful but can be

P 2 – Physics – Mains Electricity Mains electricity is useful but can be very dangerous. It is important to know how to use it safely

P 2 – Physics – Currents Cells and batteries supply current which always passes

P 2 – Physics – Currents Cells and batteries supply current which always passes in the same direction. This is called direct current (d. c. ) An alternating current (a. c. ) is one which is constantly changing direction. Mains electricity is an a. c. supply. In the UK it has a frequency of 50 cycles per second (50 hertz) UK mains supply is about 230 volts Most electrical appliances are connected to the mains using cable and a three-pin plug

P 2 – Physics - Currents Voltage Direct Current – flows in one direction

P 2 – Physics - Currents Voltage Direct Current – flows in one direction only Time 1/50 th second 230 V Time Voltage Alternating Current – changes direction 50 times every second (frequency = 50 hertz)

P 2 – Physics – The Three-Pin Plug Earth Wire Live Wire Fuse Neutral

P 2 – Physics – The Three-Pin Plug Earth Wire Live Wire Fuse Neutral Wire Insulation Cable Grip

P 2 – Physics – The Three-Pin Plug The neutral wire of a plug

P 2 – Physics – The Three-Pin Plug The neutral wire of a plug stays at a potential close to zero with respect to the earth The live wire of a plug alternates between positive and negative potential with respect to the neutral wire

P 2 – Physics - Safety If an electrical fault causes too great a

P 2 – Physics - Safety If an electrical fault causes too great a current the circuit should be switched off by a fuse or a circuit breaker When the current in a fuse wire exceeds the rating of the fuse it will melt, breaking the circuit Appliances with metal cases are usually earthed The earth wire and fuse together protect the appliance and the user

P 2 – Physics - Earth wires are always used if an appliance has

P 2 – Physics - Earth wires are always used if an appliance has a _____ case. If there is a _____ in the appliance, causing the live wire to ______ the case, the current “_______” down the earth wire and the ______ blows. Words – fuse, fault, metal, surges, touch

P 2 – Physics - Fuses are _______ devices. If there is a fault

P 2 – Physics - Fuses are _______ devices. If there is a fault in an appliance which causes the ____ and neutral (or earth) wire to cross then a ______ current will flow through the _____ and cause it to _____. This will break the _______ and protect the appliance and user from further _____. Words – large, harm, safety, melt, live, circuit, fuse