Question

(a) explain, why fuse wire is made of a tin-lead alloy and not copper? (b) a domestic circuit has 5a fuse. how many bulbs of rating 100w, 220v can be safely used in this circuit? justify your answer.

Answer 1

Fuse wire is made of a tin-lead alloy and not copper because of the following reasons:1. They have high resistance due to high resistance the wire heats up quickly, when large current flows.
Heating power of wire(P) = I² × R
2. They have low melting point which melts and breaks off the circuit if the current is larger than the safety limit.
b.first we need the total power that this DC connection is using so- P= V*I (where V is the P.D. & I is the current) by implying this formula in the question we get= 
P= 220 * 5= 1100 watts is the power. so, the total power is 1100 watts. now, if we want how many 60 watt bulbs this supply can use then we have to just divide the total power by 60 because one bulb has a power of 60 watts. implying this we get- 
n= 1100/60= 18.33. but since it should be whole number we should take it as 18.

Answer 2

A fuse is made of an alloy of tin (Sn) and lead (Pb) because it is important that the device acts (melts) without heating too much (so as not to produce fires or to heat nearby terminals or cables). This is only possible if the alloy melts at a moderate temperature.

The fuse acts by melting, and the components (tin and lead) that already have low melting temperature, form an alloy that has an even lower .