Question

Two fuses of same length are rated 5A and 20A.

Whcih of the fuse wires are thicker and why?

Answer 1

The fuse are selected in such a way that they melt following the Joule's law of heating whenever there is current more than the rated value.

The Joule's law of heating gives,

H = i²Rt

Where, H is the heat, i is the current, R is the resistance, t is the time.

So, a wire with more resistance will produce more heat and will melt easily. To support higher values of current the resistance should be low. Since, resistance is inversely proportional to the thickness of a wire. Thus, a fuse with higher value of rated current will have lower resistance and hence will be more thick.

We conclude, the fuse rated 20 A will be thicker than the fuse rated 5A.