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Potential Difference (Edexcel GCSE Physics)
Revision Note
Potential Difference
- The terminals of a cell make one end of the circuit positive and the other negative
- This sets up a potential difference across the circuit
- This is sometimes known as the voltage
- Potential difference is defined as:
The amount of energy transferred per unit of charge passing through the terminals
- This means that one volt (the unit of potential difference) is equivalent to one joule (the unit of energy) per coulomb (the unit of charge):
1 V = 1 J / C
- Potential difference can be calculated using the equation below:
- Where:
- V = potential difference, measured in volts (V)
- E = energy transferred, measured in joules (J)
- Q = charge moved, measured in coulombs (C)
- The equation for potential difference can be rearranged using the formula triangle below:
Energy, charge, potential difference formula triangle
Voltmeters
- Potential difference (or voltage) is measured using a voltmeter
- A voltmeter is always set up in parallel to the component being measured
- This is described as measuring voltage 'across' the component
Potential difference (voltage) can be measured by connecting a voltmeter in parallel between two points in a circuit. Here, the voltmeter is measuring the voltage across the resistor
Worked example
The normal operating voltage (potential difference) for a lamp is 6 V.Calculate how much energy is transferred in the lamp when 4200 C of charge flows through it.
Step 1: List the known quantities
- Voltage (potential difference), V = 6 V
- Charge moved, Q = 4200 C
Step 2: State the equation linking potential difference, energy and charge
- The equation linking potential difference, energy and charge is:
Step 3: Rearrange the equation for energy transferred
- Using the formula triangle, the energy transferred is given by:
E = V × Q
Step 4: Substitute the known values and calculate the energy transferred
E = 6 × 4200
E = 25 200 J
- Therefore, 25 200 J of energy is transferred in the lamp
Examiner Tip
Don't be confused by the symbol for potential difference (the symbol V) being the same as its unit (the volt, V). Learn the equation and remember especially that one volt is equivalent to 'a joule per coulomb'.
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