The current through a conductor is directly proportional to the potential difference across it, provided physical conditions such as temperature remain constant.

State the formula used to calculate resistance from potential difference and current, and define each symbol.

R = V/I, where R is resistance, V is potential difference across the component, and I is current through the component.

State the equation used to determine resistance when potential difference and current are known.

R = V/I, where R is resistance in ohms, V is potential difference in volts, and I is current in amperes.

Calculate the resistance when potential difference = 2 V, current = 4.9 A.

Resistance = 2 ÷ 4.9 = 0.408 Ω.

OCR A-Level Physics A H556

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Energy, Power and Resistance

Ohm's law and I-V characteristics

4 things to know
Papers 2 and 3

Overview

Recall questions on resistance and its unit, Ohm's law, R = V/I calculations, ohmic and non-ohmic components, the I-V characteristic of a resistor, and investigating I-V characteristics with a potential divider and spreadsheet.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is the SI unit of resistance?

Key term

What measurements are recorded when investigating the I–V characteristic of a component?

Key term

State Ohm's law.

Key term

How is resistance defined in terms of potential difference and current?

Questions from this subtopic

Each one with the model answer underneath.

1
What is the SI unit of resistance?
Model answer
The ohm (Ω).
2
State Ohm's law.
Model answer
The current through a conductor is directly proportional to the potential difference across it, provided physical conditions such as temperature remain constant.
3
How is resistance defined in terms of potential difference and current?
Model answer
Resistance is defined as the ratio of potential difference across a component to the current flowing through it.
4
State the formula used to calculate resistance from potential difference and current, and define each symbol.
Model answer
R = V/I, where R is resistance, V is potential difference across the component, and I is current through the component.
5
State the equation used to determine resistance when potential difference and current are known.
Model answer
R = V/I, where R is resistance in ohms, V is potential difference in volts, and I is current in amperes.
6
Calculate the resistance when potential difference = 2 V, current = 4.9 A.
Model answer
Resistance = 2 ÷ 4.9 = 0.408 Ω.

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