Question

The resistance of 10m long wire is 10 . Its length is increased uniformly by 25% by stretching the wire
uniformly. The resistance of wire will change to (approximately)
(A) 12.5 (B) 14.5 (C) 15.6 (D) 16.6

Answer 1

the mass, density and volume are assumed not to change
R is old radius
Rn is new radius

V = pi R^2 L

Vn = pi Rn^2 (1.25) L

so
1.25 Rn^2 = R^2

resistance = k *Length/area
new area = old are /1.25
new length = old length*1.25
so
new redistance = old resistance *1.25/(1/1.25)
or
1.5625 * old
so C