What should be the characteristic of fuse wire? A. High melting point, high specific resistance B. Low melting point, low specific resistance C. High melting point, low specific resistance D. Low melting point, high specific resistance
Hint- A fuse is a safety device consisting of a strip of wire that melts and breaks an Electric circuit if the current exceeds the safe value. It protects the circuit from overcurrent. As we know, once a fuse wire is operated, the circuit will become an open circuit and depending upon these points we will select the characteristics of the fuse wire.
Step-By-Step answer: The working of the fuse wire is simple. The fuse wire operates as normal wire in the circuit till the point when the current through the circuit is within the limit. As the current in the circuit starts increasing from the normal value and crosses the limit for which wire is designed; the wire starts heating. And in order to break the circuit or protect the equipment the wire must melt. This is only possible when the melting point of the wire is low. If the melting point of the wire is high it will take time to melt and the circuit will damage. As we know the fuse wire must have a small radius or they are thin as compared to normal wire used in the circuit. And we do now there is more ohmic loss in the thin wire as compared to thick wire. In order to prevent the ohmic loss; the specific resistance of the fuse wire must be low. Hence the correct answer is B low melting point and low specific resistance.
Note- Fuse should have a predictable fusing action, it should operate without creating harm by products, its body and support structure should not support combustion. If combustion will occur then it is a risk of setting the house or factory on fire. A fuse wire must be selected or designed with keeping all the conditions in mind.
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