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Potential Difference

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

In one line: Voltage is energy per coulomb.

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Understand it

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.

Example

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

Formula and rule

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

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

  1. 1If a battery gives 30 J to 5 C of charge, then V = 30/5 = 6 V.
  2. 2So the potential difference is 6 volt.

Method you can reuse

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

Sketch it in your answer

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

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

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

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

Common wrong answer

A common wrong answer is to write 24 V for 24 J and 6 C.

Why it loses marks: Voltage is energy per coulomb, not energy itself.

Don't mix this up

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

Exam tip

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

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Often asked as a numerical using energy and charge, or as a statement-based question about what voltage means.
  1. 1

    Enough for 1 mark

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

  2. 2

    Add for 2 marks

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

  3. 3

    Add for 3 marks

    It tells us how much energy is given to each coulomb of charge when it moves from one point to another.

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