Question

A wire of length L , area of cross section A and resistance R is stretched so that the length is double . How will the resistance and resistivity change ?
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Answer 1

Answer: 4R

Explanation: Resitivity of any wire is defined as resistance of unit length of wire per unit area of cross section. So it is always a fixed quantity.

Resistance = (resistivity)*L/A ----- (1)

Since volume of wire is always constant implies A1L1=A2L2

-> AL=A'(2L)

-> A' = A/2 -----(2)

Using (1) & (2)

R' = (resistivity)(2L)/(A/2)

-> R'=4R