# Physics - Electricity

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## Charge, Current and Voltage

Current

• The rate of flow or charge.
• Measured in Amperes (Amps).

Coulomb

• The charge of 6x10^18 electrons.
• Every coloumb is an amount of negative charge equal to 6x10^18 electrons.
• If 6x10^18 electrons flow past a point in the time of 1 second then the current is equal to 1 amp.

Potential Difference

• The amount of energy per unit charge (coulomb)

Voltage

• The voltage of a battery is equal to the energy in joules provided when a charge of one coulomb passes through the battery.
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## Resistance

• The thinner the wire, the greater the resistance.
• This is because there is less space for electrons to move and there are more collisions between the electrons and ions.
• More frequent collisions mean the temperature of the wire increases.
• The higher the temperature of the wire, the higher the resistance.

LDR resistance

• As light intensity decreases the resistance of LDR's increases.
• This means that they can be used effectively in street lights.

Resistors

• Have constant resistance.
• Ohm's law states that the current through a resistor is proportional to the potential difference provided the temperature is constant.
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## Electricity equations

energy transferred = potential difference x charge

electric charge = current x time

voltage = current x resistance

electrical power = current x voltage

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