GCSE PHYSICS
Ohm's law: V = I × R
Voltage, current and resistance, with worked examples.
The formula
potential difference (V) = current (A) × resistance (Ω), or V = I × R. Rearranged: I = V ÷ R and R = V ÷ I.
What each one means
Current is the rate of flow of charge. Potential difference (voltage) is the energy transferred per unit of charge. Resistance is how much a component opposes the current.
Series and parallel
In series, resistances add up: R = R₁ + R₂. In parallel, the total resistance is less than the smallest single resistor.
✏️ Worked example
A 12 V battery is connected to a 4 Ω resistor. What is the current?
I = V ÷ R = 12 ÷ 4 = 3 A.
🧠 Test yourself
What is the voltage across a 10 Ω resistor with 0.5 A flowing?
V = 0.5 × 10 = 5 V.
Two 6 Ω resistors in series: total resistance?
12 Ω.
What is the unit of resistance?
The ohm (Ω).
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