Basics of Electricity

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Current flows around any circuit where there is a potential difference.

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  • Current is the rate of flow of charge.
  • Electrons are charged particles which are allowed to move in metal.
  • When a potential difference is applied the electrons have the 'push' they need to move.
  • The flow of electrons is current.
  • Electrons flow from the negative terminal to the positive terminal of a circuit.
  • The current in a circuit can be measured by connecting an ammeter in series.
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  • Current moves in the opposite direction to the flow of electrons (positive to negative).
  • The equation for calculating current is:
    • Current = the charge flowing ÷ the time taken
    • I=ΔQΔtI=\frac{ΔQ}{Δt}
  • The units of current are Amps (A).

Potential Difference

The potential difference is also known as the voltage.

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A 'push'

  • The potential difference or voltage of a circuit is the amount of work done to move the charge around the circuit, per unit charge.
  • The voltage can be thought of as a 'push' that allows the current to flow around a circuit - it supplies the power to a circuit.
  • Voltage can be measured by connecting a voltmeter in parallel.
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  • Voltage is the work done per unit charge. The equation for voltage is:
    • Voltage = work done ÷ the charge flowing
    • V=WQV=\frac{W}{Q}
  • The units for potential difference are Volts (V)


Resistance is how hard it is to get a flow of electrons through a material.

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Resistance to motion

  • Current is electrons flowing around a circuit.
  • If the current had to travel through a component which has resistance then some work has to be done to 'push' the electrons through it.
  • There is always a voltage drop across components with resistance.
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Ohm's law

  • Ohm's law relates the current, voltage and resistance. The equation for Ohm's law is:
    • Voltage = current x resistance
    • V=IRV=IR
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Calculating resistance

  • Ohm's law can be rearranged to allow us to calculate resistance:
    • Resistance = voltage ÷ current
    • R=VIR=\frac{V}{I}

Jump to other topics

1Measurements & Errors

2Particles & Radiation


4Mechanics & Materials


6Further Mechanics & Thermal Physics (A2 only)

7Fields & Their Consequences (A2 only)

8Nuclear Physics (A2 only)

9Option: Astrophysics (A2 only)

10Option: Medical Physics (A2 only)

11Option: Engineering Physics (A2 only)

12Option: Turning Points in Physics (A2 only)

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