Question

If a copper wire is stretched so that its length increases by `20%` then what is the percentage increase in its resistance (assuming its volume remaing constant) ?
A. `10%`
B. `21%`
C. `44%`
D. `120%`

Answer 1

Correct Answer - C
`(R)/(R_(o))=((l)/(l_(o)))^(2)=((1.2l)/(l))^(2)`
`R_(f)=1.44R_(o)`
`therefore%"Changing in resistance"=(1.44R_(o))/(R_(o))xx100=0.44xx100=44%.`