The function of a fuse in an electric circuit is to

Step 1: Analyze the question The question asks about the purpose of a fuse in a circuit. This is a basic electricity and safety concept.

Step 2: The concept A fuse is a safety device containing a thin wire made of a material with a low melting point (such as tin-lead alloy). It is connected in series with the appliance or circuit it protects.

• Under normal conditions, the current is within the safe rating, and the wire stays intact.
• If the current becomes too large (due to a short circuit or overload), the heating effect of the current (H = I²Rt) makes the wire get hot, melt, and break the circuit.
• This stops the flow of current and prevents damage to appliances, overheating of wires, and fire.

Step 3: Evaluate each option

• A. Break the circuit when the current exceeds a certain value. Correct. This is exactly what a fuse does.
• B. Save energy by reducing voltage. Wrong. A fuse does not change voltage or save energy. Transformers change voltage.
• C. Ensure that the current exceeds a certain value. Wrong. This is the opposite of a fuse's purpose, because it protects against excess current.
• D. Save energy by reducing the current. Wrong. A fuse does not regulate or reduce current. It simply cuts it off when it is too high.

Step 4: Answer

Tip: Think "fuse = safety valve." It sacrifices itself (melts) to protect the circuit. Also remember that a fuse is always connected in the live wire, in series with the appliance. In calculations, choose a fuse rating slightly higher than the normal working current (I = P/V). For example, a 1000 W appliance on 240 V draws about 4.2 A, so a 5 A fuse is suitable.