A fuse with a circular cross - sectional radius of ` 0.15 mm` blows at `15 A`. What should be the radius of the cross section of a fuse made of the same material that blows at `30 A`?

Explanation

Heat produced = heat loss through surface of wire
`I^(2) R = H 2 pirl`
where `H` is the heat loss per unit surface area of the wire .
` I^(2) (rhol)/(a) = H 2 pirl`
put `a = pir^(3)`, therefore `I^(2) prop r^(2)`
or `((15)/(30))^(2)= ((0.15)/(r ))^(3) or r = 0.238 mm`