Resistance
1 guided lesson · 9 checks · 2. Electricity → Current, Potential Difference & Resistance
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Calculating current, resistance & potential difference
Squeeze a garden hose and the flow drops; leave it open and the flow soars. Resistance does to charge exactly what your hand does to the water. This lesson defines the ohm, sets the see-saw between resistance and current, and assembles the equation V = I × R that ties all three quantities together.
What you know already
Every component, even a plain copper wire, pushes back a little against the current trying to pass through it. That push-back is resistance. This note defines the ohm, shows how resistance throttles the current at a fixed voltage, and assembles the equation linking voltage, current and resistance that solves most simple circuits.
Key points of understanding
- Resistance describes how strongly a component opposes the flow of current through it.
- Resistance is measured in ohm units (Ω); one ohm lets one volt drive one amp through a component.
- For a fixed voltage, a higher resistance means a smaller current, and a lower resistance means a larger one.
- The three quantities are linked by V = I × R.
- Copper wiring has a very low resistance, which is why it counts as a good conductor.
- In exam circuits the wires, ammeters and cells are taken to have zero resistance.
A greater resistance means there is a lower current and vice versa
Formula triangle for the voltage, current and resistance equation
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1.Calculating current, resistance & potential difference
Squeeze a garden hose and the flow drops; leave it open and the flow soars. Resistance does to charge exactly what your hand does to the water. This lesson defines the ohm, sets the see-saw between resistance and current, and assembles the equation V = I × R that ties all three quantities together.
A greater resistance means there is a lower current and vice versa
Formula triangle for the voltage, current and resistance equation
Key points
- Resistance describes how strongly a component opposes the flow of current through it.
- Resistance is measured in ohm units (Ω); one ohm lets one volt drive one amp through a component.
- For a fixed voltage, a higher resistance means a smaller current, and a lower resistance means a larger one.
- The three quantities are linked by V = I × R.
- Copper wiring has a very low resistance, which is why it counts as a good conductor.
- In exam circuits the wires, ammeters and cells are taken to have zero resistance.
First pass
Resistance is the brake on the current: more ohms means less flow for the same push.
Analogy — A narrow door in a busy corridor — the wider the door (lower resistance), the more people (current) get through.
Exam pointer — Use Ω for ohms in your working, and keep V, A and Ω labelled in every substitution.
Going deeper
The equation is a see-saw: at fixed voltage, current and resistance move in opposite directions, because I = V ÷ R.
Analogy — A credit limit: the voltage is your budget, the resistance is the price of goods, and the current is how much you can buy.
Exam pointer — Assume wires, ammeters and cells have zero resistance unless a question says otherwise — only the named components count.
Checks
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