# Stretching a Thin Wire

Electricity and Magnetism Level 2

An engineer is measuring the width of an expanding crack in a wall. He fixes a thin piece of uniform wire, with its ends affixed to either side of the crack as shown in the diagram and measures its resistance $$R$$. The crack widens and the wire's length increases by 40%. The wire's volume remains constant. In percentage, how much has $$R$$ increased?

Assume that the wire remains uniform and ignore any 'leaks' of current to the wall or surroundings.

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