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Fuse

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

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Student-friendly explanation

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.

How to write this in exams

  1. 1

    Start with the exact idea

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

  2. 2

    Then show how to use it

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

  3. 3

    Add one concrete example

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

  4. 4

    Avoid this incomplete answer

    A common wrong answer is to say the fuse increases current during overload. That is wrong because the fuse is meant to stop current, not raise it.

Definition

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

Example

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

Rule to remember

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.

Memory hook

Fuse saves the circuit by melting first.

Examples and method

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 to apply

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

Diagram support

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

How CBSE asks it

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

Avoid common mistakes

Common confusion

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

Common wrong answer

A common wrong answer is to say the fuse increases current during overload. That is wrong because the fuse is meant to stop current, not raise it.

Exam tip

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

Quick check

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

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.

Answer writing and exam use

1-mark answer

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

2-mark answer

A fuse is a safety device connected in a circuit to protect it from excessive current. 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. If an overload occurs in an iron circuit, the fuse melts and stops the current before the wires overheat.

3-mark answer

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. 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. 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. Often asked as a safety question, a reason-based question, or a diagram question about where the fuse is connected. A common wrong answer is to say the fuse increases current during overload. That is wrong because the fuse is meant to stop current, not raise it.
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