The material used for fuse must have

Question

Examoogle · Accepted Answer

low melting point and high specific resistance

Explanation: A fuse is a protective device designed to interrupt an electrical circuit when current exceeds a predetermined limit. To perform this function effectively, it must melt quickly under overload conditions, necessitating a low melting point, and ensure heat generation at the rated current is manageable, requiring appropriate resistive properties.

Working Principle: The principle of operation is based on the heating effect of electric current, defined by Joule's Law $H = I^2Rt$. A high specific resistance ensures that even with a short length, the fuse wire generates sufficient heat ($I^2R$) to reach its melting point rapidly during a fault. A low melting point ensures that the wire breaks or 'blows' quickly, thereby isolating the faulted circuit segment from the supply.

Key Formulas: $H = I^2Rt$ — Joule's Law of heating; $R = \rho \frac{L}{A}$ — Resistance formula where $\rho$ is specific resistance

Key Points: The fuse wire must act as a weak point in the circuit to protect expensive components.; Common materials used for fuses include lead, tin, zinc, or alloys of these metals.; Copper is generally avoided for low-current fuses due to its high melting point, though it is used in high-voltage HRC fuses.

Advantages: Simple and inexpensive protection mechanism.; Highly reliable as it does not rely on complex mechanical parts or sensors.

Disadvantages: Requires manual replacement after operation.; Cannot be used for multiple operations unlike a Circuit Breaker (MCB).

Applications: Domestic wiring protection.; Industrial control panels.; Automotive electrical systems.

Additional Info: High specific resistance allows the fuse to be compact while maintaining the required resistance.. Option B is incorrect because low specific resistance would require a very long or very thin wire to generate heat, which is physically impractical.. Option C is incorrect because a high melting point would prevent the fuse from melting during an overload, defeating the purpose of protection.

Answer: A is correct — The fuse material must possess a low melting point to ensure rapid breaking and a high specific resistance to generate sufficient heat during overload conditions.

Exam Tip: Always remember that fuses protect against overcurrent, while relays and MCBs are preferred for applications requiring repetitive switching or adjustable settings.

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