P5 Revision Summary

Page 1

The build up of static electricity is caused by friction. When

two insulating materials are rubbed together, electrons are transferred (moved)

from one material to the other.

Two things with opposite charges are attracted to each other and two things with like charges will repel each other.

When synthetic clothes are dragged over each other (like in a tumble dryer) or over your head,electrons get scraped off,leaving static charges on both parts and that leads to the inevitable- attraction (they stick together and cling to you) and little sparks or shocks as the charges rearrange themselves.

The free electrons in metals can move freely through the metal, allowing metals to be good conductors of electricity.

Current is a flow of electrons. Current will only flow through a component if there's a voltage across that component. Voltage is the driving force that pushes the current around a circuit. Resistance is caused by things in the circuit (e.g lamps) that resist the flow of electrons (slows the charge down).

If you increase the voltage then more current will flow.

The power of an appliance measures the rate at which energy is transferred.

Power = Voltage x Current

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Page 84

Another name for voltage is Potential Difference,it

is a measure of how much energy is transferred to or from each charge as it

moves between two points in a circuit.

Page 85

12V ÷ 2.5A = 4.8Ω

A light dependent resistor or LDR is a special type of resistor that changes its resistance depending on how much light there is: in bright light,the resistance falls and in darkness the resistance is highest e.g automatic night lights.

A1= 0.2A V1=7Ω x 0.2A = 1.4V V2= 2Ω x 0.2A= 0.4V 1.4V + 0.4V= 1.8V 12V-1.8V= 10.2V - V3 So, R1= 10.2V ÷ 0.2A= 51Ω

In a series circuit potential difference (P.D) of the supply is shared between the various components. so the P.D round a series circuit always adds up to the P.D across the battery. This is because the total work done on the charge by the battery must equal the total work done by the charge on the components.

if you add more cells into a series circuit you get a bigger voltage because each charge in the circuit passes through all the cells and get a 'push' from each cell in turn.

In series circuits the total resistance is just the sum of the individual resistances. the resistance of two or more is bigger than just one because the battery has to push charge through all of them. Where as in a parallel circuit total resistance is always less then the branch of the smallest resistance. the resistance is lower because the charge has more than one branch to take- only some of the charge will flow along each branch.

0.2A because the current will be shared between the two lamps.

The UK mains electricity is supplied at 230 volts. The mains electricity is an AC supply as the current is constantly changing direction and because it is easier to generate than DC and is easier/simpler to distribute over long distances.

Electromagnetic induction is creating a voltage (and maybe a current), in a conductor by moving a magnet in or near a coil of wire.

A generator is a device that is used to move electrons through a conductor to give electric power. It does this by using a magnet that forces electrons to move along a wire at a steady rate while putting pressure on them.

With the help of a generator, the electrons can transmit electric energy from one point to another. The difference in the number of electrons and the pressure that the generator applies is what creates the different electric currents. The generator spins at a certain number of rotations per minute.

Add an iron core inside the coil, increase the strength of the magnetic field,increase the speed of rotation and increase the number of turns on the coil.

Vp/Vs = Np/Ns

500 ÷ 20 = 25 x 9= 225V

If a current carrying wire runs parallel to the lines of force of the magnetic field,it wont experience any force at all.

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The split ring commutator reverses the direction of the current every half-turn to keep the coil rotating continuously in the same direction. This is important because otherwise the direction of the force would reverse every half turn and the coil would change direction every half turn instead of fully rotating.

in a DVD player, the axles attached to the bit the DVD sits on to make it spin. Electric cars and trains have their wheels attached to axles. Electric motors spin the platters of a computer hard disc drive. Domestic

appliances such as washing machines, fridges and vacuum cleaners all use

electric motors.