# Current electricity

This is the 'current electricity' topic from AQA Double Award Physics exam and hopefully it'll help or it may just calm you down.

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## Describing the components in a circuit

Bulb - converts electric energy into light energy

Voltmeter - It measures the potential difference across a component.

Ammeter-Measures the current (number of electrons that pass every second).

Cell/battery-'pushes' electrons round the circuit

Switch-completes/breaks the circuit.

Diode-allows the current to go in one direction

Resistor-limits the current in a circuit

Variable resistor-Varies the current in a circuit.

Fuse-designed to melt/break the circuit when too much current goes through it.

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## Describing the components in a circuit CONTINUED

Heater-Converts the electric energy to thermal energy.

Thermistor-lowers its resistance as the temperature increases. E.g. kettle

LDR [light dependant resistor] - as the light intesity increases, the resistance of the circuit decreases.

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## Series circuits

Add the resistance in a series circuit.

Current is the same all the way round in a series circuit.

Voltage is shared between the components in a series circuit.

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## Parallel circuits

Current is different in a parallel circuit because it may split up at a junction.

The voltage is the same across each component.

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## How is resistance calculated?

Resistance (ohms) = voltage (V) /  current (A)

1. Type -poor conductors, high resistance which means no current.

2.Length -lectrons collide more often in a long wire as atoms collide more often in a long wire than shorter.

3.Thickness -thin wire has more resistance as electrons more likely to collide with (metal) ions. Thick wire has less resistance and a thin wire has more resistance.

4. Temperature- the hotter the wire, the greater the resistance as the increased vibrations of electrons cause them to have a larger chance of ions capturing electrons.

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