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Potential Difference

Potential difference is the work done per unit charge between two points in a circuit.

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Student-friendly explanation

It tells us how much energy is given to each coulomb of charge when it moves from one point to another. A higher potential difference means a stronger push on charges. The SI unit is volt.

How to write this in exams

  1. 1

    Start with the exact idea

    Potential difference is the work done per unit charge between two points in a circuit.

  2. 2

    Then show how to use it

    1. Identify energy or work done in joules. 2. Identify charge in coulombs. 3. Use V = W/Q. 4. Divide and write the answer in volts.

  3. 3

    Add one concrete example

    A 9 V cell gives 9 J of energy to each coulomb of charge passing through it.

  4. 4

    Avoid this incomplete answer

    A common wrong answer is to write 24 V for 24 J and 6 C. That is wrong because voltage is energy per coulomb, not energy itself.

Definition

Potential difference is the work done per unit charge between two points in a circuit.

Example

A 9 V cell gives 9 J of energy to each coulomb of charge passing through it.

Rule to remember

V = W/Q, where V is potential difference, W is work done or energy, and Q is charge.

Memory hook

Voltage is energy per coulomb.

Examples and method

Worked example

If a battery gives 30 J to 5 C of charge, then V = 30/5 = 6 V. So the potential difference is 6 volt.

Method to apply

1. Identify energy or work done in joules. 2. Identify charge in coulombs. 3. Use V = W/Q. 4. Divide and write the answer in volts.

Diagram support

Show a battery with two marked points and a voltmeter connected across those two points in parallel.

How CBSE asks it

Often asked as a numerical using energy and charge, or as a statement-based question about what voltage means.

Avoid common mistakes

Common confusion

Students often confuse potential difference with current or treat voltage as total energy.

Common wrong answer

A common wrong answer is to write 24 V for 24 J and 6 C. That is wrong because voltage is energy per coulomb, not energy itself.

Exam tip

Remember that voltage is always between two points, not at a single point alone.

Quick check

A cell transfers 24 J of energy to 6 C of charge. What is the potential difference?

The potential difference is 4 V because V = W/Q, so 24 divided by 6 gives 4 volt.

Answer writing and exam use

1-mark answer

Potential difference is the work done per unit charge between two points in a circuit.

2-mark answer

Potential difference is the work done per unit charge between two points in a circuit. V = W/Q, where V is potential difference, W is work done or energy, and Q is charge. A 9 V cell gives 9 J of energy to each coulomb of charge passing through it.

3-mark answer

It tells us how much energy is given to each coulomb of charge when it moves from one point to another. A higher potential difference means a stronger push on charges. The SI unit is volt. V = W/Q, where V is potential difference, W is work done or energy, and Q is charge. If a battery gives 30 J to 5 C of charge, then V = 30/5 = 6 V. So the potential difference is 6 volt. Often asked as a numerical using energy and charge, or as a statement-based question about what voltage means. A common wrong answer is to write 24 V for 24 J and 6 C. That is wrong because voltage is energy per coulomb, not energy itself.
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