Resistance & Ohm's Law
Resistance & Ohm's Law
- Resistance compares the p.d. across a component with the current through it.
- Ohm's law is a separate statement about when that ratio stays constant.
Resistance at one operating point
Definition
1 markWhat is meant by resistance?
Model answer: The ratio of the potential difference across a component to the current through it.
Symbols
- = resistance (\Omega)
- = p.d. across the component (V)
- = current through the component (A)
- One ohm is the resistance when 1 V produces a current of 1 A.
- To measure resistance, place the ammeter in series and the voltmeter in parallel across the component.
The constant-temperature condition
Definition
2 marksWhat is meant by Ohm's law?
Model answer: The current in a conductor is directly proportional to the potential difference across it, provided its temperature and other physical conditions remain constant.
- If a conductor obeys Ohm's law, doubling doubles , so remains constant.
- can be used for every component at a chosen operating point. It does not prove that the component obeys Ohm's law.
Your turn9702/11/M/J/25 Q32
Which expression defines resistance? [1] (9702/11/M/J/25 Q32)
A current ÷ p.d.
B current × p.d.
C p.d. ÷ current
D resistivity × length
Show worked answer
C. Resistance is the potential difference across the component divided by the current through it: .