A fuse wire with a circular cross-sectional radius of 0.02 mm blows with a current of 5 ampere. For what current, another fuse wire made from the same material with cross-sectional radius of 0.04 mm will blow?

The fuse current (I) is proportional to the square root of the cross-sectional area. Since area is proportional to the square of the radius, doubling the radius increases I by √4 = 2, giving = 5 × 2¹.5 = 14.7 A.
Answer: (a) 14.7 A