Question

1. A wire of 3ohm resistance and 15cm in length is stretched to 45cm length. Calculate (i) new resistance
and (ii) new resistivity. Assume wire has uniform cross-sectional area 0.5 x 10^-7ohm m.
​

Answer 1

original wire,

R= 3ohm , l= 0.15m

a = 0.5×10^-7

now,

R = p × l/a

=》3 = p × 0.15

-------------------

0.5×10^-7

=》p = 10^-6 (resistivity)

new wire,

p=10^-6 ,l= 0.45m

a= 0.16×10^-7

now,

R =p × l/a

=》R = 10^-6 × 0.45

---------------------

0.16 × 10^-7

=》 R = 30 ohm (answer)

(approx.)

resistance remain same with same material i.e,

p = 10^-6 (answer)