The unit for
ΔL/L
is

the unit for ΔL/L is "unitless".

Explanation:

Given;

ΔL/L

by physics convection, the above parameters can be defined as;

delta L (ΔL) is change in length, with SI unit as meters (m),

L is the original length of the material, with SI unit as meters (m)

The ratio of the change in length to the original length has no unit since both units cancel out during the division.

This ratio (ΔL/L), is also called tensile strain and it has no unit.

Therefore, the unit for ΔL/L is "unitless".

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