Science (086) — AI-generated practice question

A fuse wire is made of a metal or alloy with a low melting point (e.g., aluminium, lead, or their alloys). During normal operation, the current is within the rated value, so the heat produced (H = I²Rt) is not enough to melt the wire.

When an excessive current flows, heat produced increases rapidly (proportional to I²), raising the fuse wire's temperature above its low melting point. The wire melts quickly, breaking the circuit and protecting the appliance.

The fuse is connected in series so that the entire circuit current passes through it. The material's low melting point ensures fast response to overload, while its rated thickness ensures it survives normal current without melting.

Source: Chapter 11, Section 11.7.1

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• Examiners expect three distinct points: (1) material has low melting point, (2) normal current → insufficient heat → wire intact, (3) excess current → heat ∝ I² rises sharply → wire melts and breaks circuit.
• Mentioning Joule's law (H = I²Rt) scores a mark and shows understanding.
• "Series connection" is a useful design point but don't spend too many words on it — focus on material + heating effect.
• Avoid vague phrases like "it melts easily" — always link to low melting point and Joule's heating for full marks.