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P5 ­ Electric Circuits
Static Electricity
Static electricity is all about charges which are not free to move; causing them to build up in one place
and leave to sparks or shocks when they finally do move. This build-up of static is caused by friction.

When two insulating materials are…

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Resistance: (R) is caused by things in the circuit (such as components) that resist the flow of charge
(slows the charge down). Its units are ohms, .

There is a balance as the voltage is trying to push the current round the circuit, and the resistance is
opposing it ­…

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The Standard Test Circuit

This circuit is used for testing components.

The component, the ammeter and the variable
resistor are all in series, meaning that they can
be put in any order in the main circuit.

The voltmeter can only be placed in parallel
around the component under test. If…

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Calculating Resistance

At a constant temperature the resistance of a component is steady and is equal to the inverse of the
gradient of the line, or 1/gradient. In other words, the steeper the graph the lower the resistance.

When electrons move through a resistor, they collide with stationary
positive ions…

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The total resistance is just the sum of the individual resistances. The resistance of two (or more)
resistors in series is bigger than the resistance of just one of the resistors on its own because the
battery has to push charge through all of them.

The bigger the resistance…

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of the charge will flow along each branch. A circuit with two resistors will have a lower resistance
than a circuit with either of the resistors by themselves ­ which means it will have a higher current.

Cell current

Cells connected in parallel circuits increase the total current in the…

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If you want a bigger peak voltage and current you could do one of these four things:

Transformers are used to change the size of the voltage ­ they use electromagnetic induction to step
up or step down the voltage. They have two coils of wire, the primary and…

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Current Carrying Wires

There is a magnetic field around a straight, current carrying wire. The field is made up of concentric
circles with the wire in the centre.

Because of its magnetic field, a current carrying wire or coil can exert a force on another current
carrying wire or coil,…

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These forces are just the usual forces which act on any current carrying wire in a magnetic field.
Because the coil is on a spindle and the forces act one up and one down, it rotates. The split ring
commentator is a clever way of swapping the contacts every half…


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