Current, Potential Difference and Resistance
Learn how current, potential difference and resistance differ, how each is measured, and how they are linked in AQA GCSE Physics exam calculations.
Current is the flow of electrical charge, potential difference pushes charge around a circuit, and resistance opposes the flow of charge.
Current
Current measures the rate of flow of electrical charge. It tells you how much charge passes a point each second.
Current is represented by III and measured in amperes, A\text{A}A. It is linked to charge flow and time by:
Q=ItQ = ItQ=ItAn ammeter measures current and is connected in series with a component. In a single closed loop, current has the same value at every point.
Potential difference
Potential difference is the energy transferred per unit of charge between two points in a circuit. It provides the push that makes charge flow. A source, such as a cell, provides the potential difference needed for charge to flow in a closed circuit.
Potential difference is represented by VVV and measured in volts, V\text{V}V. A potential difference of 1 V1\,\text{V}1V transfers 1 J1\,\text{J}1J of energy per coulomb of charge.
A voltmeter measures potential difference and is connected in parallel across a component.
Resistance
Resistance describes how strongly a component opposes the current. For a given potential difference, a larger resistance produces a smaller current.
Resistance is represented by RRR and measured in ohms, Ω\OmegaΩ.
The three quantities are linked by:
V=IRV = IRV=IRWorked example
A resistor has a potential difference of 12 V12\,\text{V}12V across it and a current of 3 A3\,\text{A}3A. Calculate its resistance.
Rearrange the equation:
R=VIR = \frac{V}{I}R=IVSubstitute the values:
R=123=4 ΩR = \frac{12}{3} = 4\,\OmegaR=312=4ΩTherefore, the resistance is 4 Ω4\,\Omega4Ω.
Key comparison
Current describes charge flow; potential difference describes energy transferred per charge; resistance describes opposition to current. Current passes through a component, while potential difference is measured across it.
Common exam mistake
Do not say that current is “used up” by a component. Charge continues to flow around a closed circuit. Components transfer energy from the charges and provide resistance to the current.
This explanation assumes AQA GCSE Physics Higher Tier, although this core content is also assessed at Foundation Tier.
