A fuse wire must be
- A.conducting and of low melting point
- B.conducting and of high melting point
- C.insulator and of high melting point
- D.insulator and of low melting point
Correct answer
Explanation
The correct answer is A, conducting and of low melting point. A fuse must carry the normal current, so it must conduct, and it must melt quickly when the current becomes too large.
A fuse is a safety device connected in series with the live wire of a circuit. When a short circuit or overload sends excess current through it, the heat produced, which grows with the square of the current, melts the thin wire and breaks the circuit before the appliances or the house wiring can be damaged. Fuse wire is usually an alloy of tin and lead, chosen for its low melting point. Today miniature circuit breakers often do the same job and can simply be reset.
B is wrong because a wire with a high melting point would not melt in time and the circuit would not be protected. C is wrong because an insulator cannot carry current at all, so the circuit would never work. D is wrong for the same reason: an insulating fuse would block even the normal current.
Exam tip: fuse wire, tin–lead alloy, low melting point, joined in series with the live wire.
Practice Questions
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- B.2 and 4
- C.1 and 3 only
- D.1 only
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