One ohm is the resistance of a component in which a potential difference of one volt drives a current of one ampere, so 1 Ω = 1 V A⁻¹.

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

Why does the statement of Ohm's law include the condition that the temperature stays constant?

The resistance of most conductors changes with temperature, so if a large current warms the conductor the ratio of potential difference to current alters and the proportionality is destroyed.

A potential difference of 12 V drives a current of 0.40 A through a resistor. Calculate its resistance.

The resistance is R = V/I = 12 ÷ 0.40 = 30 Ω, and 0.40 A × 30 Ω returns the 12 V as a check.

CCEA A-Level Physics 1210

Physical Quantities, Scalars and Vectors

Topic overview Physical quantities and SI base units Prefixes and standard form Scalars and vectors Resolving vectors and finding resultants Coplanar forces in equilibrium

Moments and Equilibrium

Topic overview Moment of a force Centre of gravity The principle of moments Determining unknown masses using moments

Linear Motion and Dynamics

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Newton's Laws of Motion

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Linear Momentum and Impulse

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Work, Energy and Power

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Current, Charge and Potential Difference

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Resistance and Resistivity

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Internal Resistance and Potential Dividers

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Waves

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Refraction

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Lenses

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Superposition, Interference and Diffraction

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Quantum Physics

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Wave-Particle Duality

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Astronomy

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Practical Skills and Data Analysis

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Deformation of Solids

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Thermal Physics

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Uniform Circular Motion

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Simple Harmonic Motion

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The Nucleus and Radioactive Decay

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Gravitational Fields

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Capacitors

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Fundamental Particles

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Resistance and Resistivity

Resistance and Ohm's law

3 things to know
Unit AS 1

Overview

Resistance of a component, equation defining resistance and give the unit of each symbol and ohm's law.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

State the equation defining resistance and give the unit of each symbol.

Key term

Define the resistance of a component.

Key term

Define the ohm.

Questions from this subtopic

Each one with the model answer underneath.

1
Define the resistance of a component.
Model answer
The resistance of a component is the potential difference across it divided by the current through it, R = V/I.
2
State the equation defining resistance and give the unit of each symbol.
Model answer
The equation is R = V/I, where R is the resistance in ohms, V the potential difference in volts and I the current in amperes.
3
Define the ohm.
Model answer
One ohm is the resistance of a component in which a potential difference of one volt drives a current of one ampere, so 1 Ω = 1 V A⁻¹.
4
State Ohm's law.
Model answer
The current through a conductor is directly proportional to the potential difference across it, provided the temperature and other physical conditions remain constant.
5
Why does the statement of Ohm's law include the condition that the temperature stays constant?
Model answer
The resistance of most conductors changes with temperature, so if a large current warms the conductor the ratio of potential difference to current alters and the proportionality is destroyed.
6
A potential difference of 12 V drives a current of 0.40 A through a resistor. Calculate its resistance.
Model answer
The resistance is R = V/I = 12 ÷ 0.40 = 30 Ω, and 0.40 A × 30 Ω returns the 12 V as a check.

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Resistance and Ohm's law

Overview

What you need to know

State the equation defining resistance and give the unit of each symbol.

Define the resistance of a component.

Define the ohm.

Questions from this subtopic

Define the resistance of a component.

State the equation defining resistance and give the unit of each symbol.

Define the ohm.

State Ohm's law.

Why does the statement of Ohm's law include the condition that the temperature stays constant?

A potential difference of 12 V drives a current of 0.40 A through a resistor. Calculate its resistance.

Other ways to work this

What is inside Levo

The 3-step method, run for you

Cram a whole paper in one sitting

Blank Blitz makes facts automatic

Build It gets the exam shape right

Test It catches misconceptions

Brain Breaks between sessions

Every question in Resistance and Resistivity, on a schedule.