Ohm's Law & Resistance
Year 9 ⚡ Electricity & Magnetism Apply V = IR; describe factors affecting resistance.
⚡ Ohm's Law
Ohm's Law states that the current through a conductor is proportional to the voltage across it (at constant temperature).
⚡ Ohm's Law
$$V = IR$$
$V$ = voltage (V) · $I$ = current (A) · $R$ = resistance (Ω)
Use the VIR triangle: cover the quantity you want to find.
🔧 Resistance Factors
The resistance of a wire depends on: its length (longer → more resistance), its cross-sectional area (wider → less resistance), its material, and its temperature.
Ohmic conductor: Metal wire at constant temperature — V-I graph is a straight line through the origin.
Non-ohmic: Filament bulb — resistance increases as it heats up; V-I graph is curved.
🔗 Resistors in Series & Parallel
Combined Resistance
$$\text{Series: } R_T = R_1 + R_2 \qquad \text{Parallel: } \frac{1}{R_T} = \frac{1}{R_1} + \frac{1}{R_2}$$
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⚡ Ohm's Law Calculator