Potential difference & resistance (Edexcel GCSE Physics): Revision Notes
Potential difference & resistance
Potential Difference and Resistance
In addition to current, we can also measure the potential difference (pd) and resistance in a circuit.
Potential difference is the driving force that causes electric charges to flow through a circuit. It is measured in volts (V) and can be measured using a voltmeter. A voltmeter must be connected in parallel with the component for which you want to determine the potential difference.
Resistance slows down the flow of electrical charges in a circuit. It is measured in ohms (Ω).
The current, potential difference and resistance are related by the equation:
Where:
- V is the potential difference in volts (V)
- I is the current in amps (A)
- R is the resistance in ohms (Ω)
Resistance
As electrical charge flows through a circuit, it encounters resistance. This resistance causes energy to be transferred, some usefully and some as heat.
Units:
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Energy - J, joules
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Charge, c, coulombs
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Potential v, voltage Electrons collide with ions in the resistor, making the ions vibrate and heat up. As the resistor heats up, it becomes harder for electrons to pass through, reducing the current and potential difference.
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If the resistor gets too hot, the current stops. However, thermistors behave differently: their resistance decreases as they warm up.
Example: Calculating Current from Potential Difference and Resistance If the potential difference across a 20 Ω resistor is 8 V, what is the current through the resistor?
So, to find the current for :