C
CraftExam
medium importancemedium difficulty5 min

Fuse

A fuse is a safety device connected in a circuit to protect it from excessive current.

In one line: Fuse saves the circuit by melting first.

Practice This Concept

Understand it

A fuse wire has a low melting point and is connected in series, usually in the live wire. If the current becomes too large, the fuse wire gets heated and melts, breaking the circuit. This protects appliances and wiring from damage.

Example

If an overload occurs in an iron circuit, the fuse melts and stops the current before the wires overheat.

Formula and rule

A fuse is connected in series in the live wire.

It must melt at a current slightly above the safe working current of the circuit.

See it worked out

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

Worked example

If a 5 A circuit is protected by a 5 A or slightly higher rated fuse, the fuse melts during overload and opens the circuit before damage occurs.

Method you can reuse

  1. 1Identify the safe current of the circuit.
  2. 2Place the fuse in series in the live wire.
  3. 3Choose a rating slightly above normal working current.
  4. 4Explain that excess current melts the fuse wire and breaks the circuit.

Sketch it in your answer

Show a fuse symbol in the live wire path, before the appliance, so the whole circuit is protected when it melts.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

Why is a fuse wire made thin and given a low melting point?

Think first, then show answer
A fuse wire is thin and has a low melting point so it melts quickly when current becomes too large, breaking the circuit and protecting the appliance.

Common wrong answer

A common wrong answer is to say the fuse increases current during overload.

Why it loses marks: The fuse is meant to stop current, not raise it.

Don't mix this up

Students sometimes place the fuse in parallel or think it allows extra current to pass safely.

Exam tip

Always mention series connection, live wire, and melting due to excess current in answers.

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 safety question, a reason-based question, or a diagram question about where the fuse is connected.
  1. 1

    Enough for 1 mark

    A fuse is a safety device connected in a circuit to protect it from excessive current.

  2. 2

    Add for 2 marks

    Example: If an overload occurs in an iron circuit, the fuse melts and stops the current before the wires overheat.

  3. 3

    Add for 3 marks

    A fuse wire has a low melting point and is connected in series, usually in the live wire.

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