Potential difference
The current through a component depends on both the resistance of the component and the potential difference across the component.
Key fact
Potential difference (or voltage) is a measure of energy, per unit of charge, transferred between two points in a circuit. A potential difference of 1 volt means that 1 joule of work is done per coulomb of charge.
Measuring potential difference
To measure the potential difference across a component, a voltmeter must be placed in parallel with that component in order to measure the difference in energy from one side of the component to the other. Potential difference is also known as voltage and is measured in volts (V).
Energy, voltage and charge
When a charge moves through a potential difference, electrical work is done and energy transferred. The energy transferred can be calculated using the equation:
Energy transferred = charge moved × potential difference
E=QV
This is when:
- potential difference (V) is measured in volts (V)
- energy (E) is measured in joules (J)
- charge (Q) is measured in coulombs (C)
One volt is the potential difference when one coulomb of charge transfers one joule of energy.
When a charge moves through a potential difference, electrical work is done and energy transferred. The potential difference can be calculated using the equation:
potential difference = current × resistance
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This is when:
- potential difference (V) is measured in volts (V)
- current (I) is measured in amps (A)
- resistance (R) is measured in ohms (Ω)
From the equation, it can be seen that increasing the resistance for a certain potential difference will reduce the current passing through. For example, if a variable resistor is adjusted to double its initial resistance, the current passing will be halved.
Key fact
Conductors have a low resistance. Insulators have large resistances.
