Question

A strip of copper $\left(Cu\right)$ metal is riveted to a strip of aluminium $\left(Al\right)$ metal and both strips have the same length. The two metals are then heated. What happens if coefficient of expansion ${\alpha }_{Al}>{\alpha }_{Cu}$?

• A. The strips expands without bending.
• B. The strip expands and bends towards the copper side.
• C. The strip expands and bends towards the aluminium side.
• D. The strips may or may not bend.

Answer 1

The correct option is B The strip expands and bends towards the copper side.

Given:
Coefficient of expansion of aluminium
$\left({\alpha }_{Al}\right)$ is greater than coefficient of expansion of copper $\left({\alpha }_{Cu}\right)$.

This means, per degree rise of temperature, aluminium strip will expand more than the copper strip.
And we know, for an arc having some width, outer circumference is greater than inner circumference. Therefore, aluminium will be the outer layer and copper will be the inner layer of the arc formed i.e strip bends towards the copper side.
Before heating -


After heating -