Question

What is immaterial for an electric fuse wire?

• A. Its specific resistance
• B. Its radius
• C. Its length
• D. Current flowing through it

Answer 1

The correct option is C Its length

An electric fuse wire of length l and radius r, when used in series of the circuit, can withstand the heat only if the rate of heat produced due to the current in it is equal to the rate of heat lost due to radiation. If H is the rate of the heat lost per unit area of the fuse wire, then
$H\times 2\pi rl=I^{2}R=\frac{I^2\rho l}{\pi r^2}H=\frac{I^2\rho }{2{\pi }^2{r}^3}$
Hence length is immaterial.