Question

A wire of length l and cross-sectional area a is stretched an amount δl by a force f. The strain is

Answer 1

Strain is change in length by actual length. So here the initial length is l, final length is increased by dl. So

Strain = dl/l

Strain is a dimensionless quantity. It has no unit. It is a pure ratio.

This is the answer to the given question. Remember always, strain is dimensionless.