IGCSE Physics Electricity: V=IR and Essential Circuit Calculations
IGCSE Physics electricity and V=IR (Ohm’s law) are among the most searched IGCSE topics because electricity appears in almost every Physics paper. (V = I \times R) links voltage (V), current (I), and resistance (R); you must also know how to apply it in series and parallel circuits.
Essential Electricity Formulas for IGCSE
- Ohm’s law: (V = I \times R) (and (I = \frac{V}{R}), (R = \frac{V}{I})).
- Series: Same current through each component; total resistance (R_1 + R_2 + \ldots); voltages add.
- Parallel: Same voltage across each branch; total resistance (\frac{1}{R_{\text{total}}} = \frac{1}{R_1} + \frac{1}{R_2}); currents add.
- Power: (P = I \times V) (and (P = I^2 R), (P = \frac{V^2}{R}) where applicable).
Always label circuits (currents, voltages, resistances) and show your working so you can gain method marks.
Common Question Types
- Finding current, voltage or resistance in a single component or in a circuit.
- Combined series and parallel – Simplify step by step.
- Power and energy – Using (P = IV) and (E = Pt) (or equivalent).
Practise with past paper electricity questions and draw clear circuit diagrams where required.
Worked Example and Common Errors in Circuit Questions
Example: A 12 Ω resistor has 2 A through it. Find the voltage. V = I × R = 2 × 12 = 24 V. In series, current is the same everywhere; add resistances. In parallel, voltage is the same across each branch; use 1/R_total = 1/R₁ + 1/R₂. Common errors: Wrong formula (write V=IR and rearrange correctly); mixing up series and parallel rules; wrong units (convert mA to A, kΩ to Ω); not labelling the circuit. Practise with past paper circuit questions and mark with the mark scheme to see how many marks are for method.
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