Resistance and Ohm's Law
Resistance is how much a component opposes the flow of current, and Ohm's law links it to voltage and current.
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Resistance is how much a component opposes the flow of current, and Ohm's law links it to voltage and current.
- V equals I times R
- Resistance is measured in ohms
- Longer, thinner wires have more resistance
🧠 Quick quiz
Three questions. Score 2 or more to complete the topic.
What is Resistance and Ohm's Law?
Within Physics, which covers forces, energy, waves, electricity, magnetism, light and space explained through motion and experiments, this topic explains Resistance and Ohm's Law. Physics topics explain how things move, push, heat up and carry energy, so each one here pairs a definition with a live model you can change.
Check that you can explain Resistance and Ohm's Law in your own words and give one example from everyday life. If you can do that, you have understood the core idea.
Understanding Resistance and Ohm's Law explains how the physical world behaves, from sport and transport to electricity and medicine.
Resistance and Ohm's Law in detail
Resistance opposes the flow of current and is defined as R = V/I, measured in ohms (Ω). Ohm's law says that for an ohmic conductor at constant temperature, current is directly proportional to p.d., so the I-V graph is a straight line through the origin.
Resistance of a wire increases with length and decreases with cross-sectional area, and depends on the material. A filament lamp is non-ohmic: its resistance rises as it heats up, so its I-V graph curves. To investigate, vary the p.d. with a variable resistor and record readings from an ammeter and a voltmeter.
How the interactive helps you understand Resistance and Ohm's Law
Watch the circuit in the interactive. Use any sliders or buttons it offers to change the values and see how the circuit responds.
Before you change anything, predict the result. Then change one value at a time and check whether your prediction was right. This is a quick way to build a correct mental model of Resistance and Ohm's Law.
Real-life uses and examples
- Explain everyday devices, such as brakes, lifts or chargers, using Resistance and Ohm's Law.
- Use Resistance and Ohm's Law to make sense of a practical and its results.
- Answer “explain” questions by linking Resistance and Ohm's Law to a clear cause and effect.
Common mistakes to avoid
- Forgetting that some quantities, such as force or velocity, also have a direction.
- Mixing up Resistance and Ohm's Law with a related quantity that has different units.
- Learning the definition without testing it. Use the quiz and the interactive to check that you can apply the idea.
Frequently asked questions about Resistance and Ohm's Law
What is Resistance and Ohm's Law?
Resistance is how much a component opposes the flow of current, and Ohm's law links it to voltage and current.
What are the most important points about Resistance and Ohm's Law?
The main points are: V equals I times R; Resistance is measured in ohms; Longer, thinner wires have more resistance.
Why is Resistance and Ohm's Law useful?
Understanding Resistance and Ohm's Law explains how the physical world behaves, from sport and transport to electricity and medicine.
How can I practise Resistance and Ohm's Law?
Open the interactive at the top of this page and change the controls one at a time. Predict the result before each change, then take the three-question quiz. A score of two or more marks the topic as complete on this device.
Which topics are related to Resistance and Ohm's Law?
Related topics in Physics include Components: Resistors, LDRs and Thermistors, Electromagnets, Generators and Dynamos.