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Resistance

Resistance is the opposition offered by a conductor to the flow of electric current.

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Student-friendly explanation

A conductor with higher resistance allows current to flow less easily. Resistance depends on the length, thickness, material, and temperature of the conductor. It is measured in ohm.

How to write this in exams

  1. 1

    Start with the exact idea

    Resistance is the opposition offered by a conductor to the flow of electric current.

  2. 2

    Then show how to use it

    1. Use R = V/I when voltage and current are given. 2. Compare length, area, material, or temperature when a wire is changed. 3. Decide whether resistance increases or decreases. 4. Write the final answer clearly.

  3. 3

    Add one concrete example

    A long, thin nichrome wire has more resistance than a short, thick copper wire of the same size.

  4. 4

    Avoid this incomplete answer

    A common wrong answer is to say a longer wire has less resistance because it has more material. That is incorrect; a longer path increases opposition to current.

Definition

Resistance is the opposition offered by a conductor to the flow of electric current.

Example

A long, thin nichrome wire has more resistance than a short, thick copper wire of the same size.

Rule to remember

R = V/I. For a wire of the same material, resistance increases with length and decreases with cross-sectional area.

Memory hook

Resistance means resists current.

Examples and method

Worked example

If a conductor has 12 V across it and carries 3 A, then R = V/I = 12/3 = 4 ohm.

Method to apply

1. Use R = V/I when voltage and current are given. 2. Compare length, area, material, or temperature when a wire is changed. 3. Decide whether resistance increases or decreases. 4. Write the final answer clearly.

Diagram support

Show two wires of the same material, one long and thin and one short and thick, with current arrows to compare resistance.

How CBSE asks it

Asked as comparison questions, numerical questions using V and I, or reasoning questions about wire size and material.

Avoid common mistakes

Common confusion

Students often think resistance is the amount of current, not the opposition to current.

Common wrong answer

A common wrong answer is to say a longer wire has less resistance because it has more material. That is incorrect; a longer path increases opposition to current.

Exam tip

Remember: longer wire means more resistance, and thicker wire means less resistance.

Quick check

Why does a long, thin wire usually offer more resistance than a short, thick wire?

A long, thin wire offers more resistance because current has a longer path to travel and less cross-sectional area is available for charge flow.

Answer writing and exam use

1-mark answer

Resistance is the opposition offered by a conductor to the flow of electric current.

2-mark answer

Resistance is the opposition offered by a conductor to the flow of electric current. R = V/I. For a wire of the same material, resistance increases with length and decreases with cross-sectional area. A long, thin nichrome wire has more resistance than a short, thick copper wire of the same size.

3-mark answer

A conductor with higher resistance allows current to flow less easily. Resistance depends on the length, thickness, material, and temperature of the conductor. It is measured in ohm. R = V/I. For a wire of the same material, resistance increases with length and decreases with cross-sectional area. If a conductor has 12 V across it and carries 3 A, then R = V/I = 12/3 = 4 ohm. Asked as comparison questions, numerical questions using V and I, or reasoning questions about wire size and material. A common wrong answer is to say a longer wire has less resistance because it has more material. That is incorrect; a longer path increases opposition to current.
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