Edexcel IGCSE Physics - Notes on Harder Topics

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Edexcel IGCSE Physics

Ø  Astronomy:

·      As a comet gets closer to the Sun, the gravitational forces acting on it increase and it speeds up. The opposite happens when it is at its furthest point.

Ø  Mains electricity:

·      The following hazards increase the chances of electric shocks:

§  Frayed cables, any damaged insulation can expose ‘live’ wires

§  Long cables, as they are more likely to get damaged or trip people up

§  Damage to plugs or any insulating casing on any mains operating devices

§  Water around electric sockets or mains operated devices

§  Pushing metal objects (conductors) into mains sockets – often a problem with young children, and can be solved using socket covers

·      When wiring a plug, the earth wire is in the middle, with the neutral wire on the left and the live wire on the right.

·      There are several safety features present in electrical appliances:

§  All mains wiring is double insulated with two layers of insulation. This prevents the separate conductors (earth, neutral, and live) from touching and prevents anyone from touching a ‘live’ (mains voltage) wire.

§  Some appliances (e.g. kettles, electric drills) are double insulated; as well as their wiring being insulated the outer casing of the appliance is made from an insulating material, usually plastic. This means that there is no chance of an electric shock from the casing.

§  Appliances with a metal outer casing that the user might touch must be earthed. The earth wire ensures that the outer casing is held at 0V and provides a very low resistance path for current in the event of a fault in which the live wire touches the casing. This means that the fault current will be very large and cause the fuse to blow immediately, disconnecting the live supply.

§  Fuses are fitted in plugs, and in the consumer unit next to the electricity meter. Cartridge fuses are ceramic, heat proof tubes containing a wire designed to melt when a certain current is exceeded, thereby cutting off the live supply.

§  Circuit breakers are now used in domestic consumer units rather than fuse wire or cartridge fuses, and do not need to be replaced.

·      When an electric current is passing through a wire some of the electrical energy is converted into heat. This is widely used in our homes in electric irons, cookers, kettles, and hairdryers.

·      A current in a resistor results in the electrical transfer of energy and an increase in temperature.

·      Power (P) = Current (I) x Voltage (V)

·      Energy transferred = Power x Time

·      The mains supply is alternating current (the current continuously changes direction) whereas a battery supplies direct current (current flows in the same direction all the time).

Ø  Energy and potential difference in circuits:

·      Advantages of series circuiting include a smaller voltage


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