GCSE Physics Revision — Ohm's Law
Revise Ohm's Law for GCSE Physics with a topic explanation, worked example and common mistakes. Check the board notes for specification differences.
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What is Ohm's Law?
Ohm's Law states that the current through a conductor is directly proportional to the potential difference across it, provided the temperature and other physical conditions remain unchanged. This relationship is expressed by the equation V = IR, where V is voltage, I is current, and R is resistance.
Board notes: A key law in all GCSE Physics specifications (AQA, Edexcel, OCR). Understanding which components are ohmic and non-ohmic is crucial.
Step-by-step explanationWorked examples
Worked example
A resistor has a resistance of 12Ω and the potential difference across it is 6V. What is the current flowing through it? Solution: Using Ohm's Law, I = V/R. I = 6V / 12Ω = 0.5A.
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Common mistakes
- 1Applying Ohm's Law to non-ohmic conductors. Ohm's Law only applies to components with a constant resistance, like a resistor at a constant temperature. It does not apply to filament lamps or diodes.
- 2Rearranging the formula incorrectly. A common mistake is to write I = VR or R = VI.
- 3Forgetting the condition that physical conditions (like temperature) must be constant. The resistance of many components changes with temperature.
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Frequently asked questions
What is an ohmic conductor?
An ohmic conductor is a component that obeys Ohm's Law. Its resistance is constant, so the graph of voltage against current is a straight line through the origin.
What is the relationship between current and voltage in Ohm's Law?
Current is directly proportional to voltage. This means if you double the voltage, you double the current, as long as the resistance stays the same.