Voltage & Potential Difference (Oxford AQA IGCSE Physics)

Voltage

• The voltage of a source is the energy supplied by a source in driving charges around a complete circuit

  • It is also called e.m.f. or the source of potential difference

  • It is measured in volts, V

• Voltage is supplied by:

  • A cell

  • Batteries (multiple cells)

  • Electrical generator

Potential Difference

• As charge flows around a circuit, energy is transferred to or from the charge

• The potential difference (p.d. or voltage) across a component measures the amount of energy that is transferred by the charge flowing in the circuit to the component

  • Potential difference is also measured in volts (V)

The potential difference in a circuit

Measuring potential difference

• Potential difference (or voltage) is measured using a voltmeter

• A voltmeter is always set up in parallel to the component you are measuring the potential difference across

Voltmeter in parallel

Potential Difference, Energy & Charge

• The potential difference (voltage) across a component measures the energy transfer by charges

  • Charge is measured in coulombs, C

• The unit of voltage, the volt (V), is the same as a joule per coulomb (J/C)

1 V = 1 J/C

• So, for example:

  • If a bulb has a potential difference of 3 V, every coulomb of charge passing through the bulb will lose 3 J of energy

• Potential difference is calculated using the equation:

• Where:

  • V is the potential difference measured in volts, V

  • E is energy transferred measured in joules, J

  • Q is charge flow measured in coulombs, C