Question

a wire is streched so that its length becomes 6/5 times its orignal length. if its orignal resistance is 25 ohm. find its new resistance and resistivity

Answer 1

the answer is 30 . Since resistance is directly proportional to length, new resistance R is given by

                        R=6/5 x r

where r is old resistance

R=6/5 x 25

R= 30

Answer 2

R = p L/A

R = 25 ohm

Volume of material in the conductor = LA

Vol of the conductor remains the same

Vol = AL

= A'L'

A' = AL/L'

After streching the wire

L' = 6L/5

A' = 5AL/6L

= 5A/6

Resistance of streched wire = R'

= pL'/A'

= p(6L/5) × {6 / (5A) }

R' = 36pL / 25A

R' = 36R / 25

Now Resistance ,

= 36×25 / 25ohm

= 36 Ohm