Question: A flat bimetallic strip consists of a strip of aluminum riveted to a strip of iron. When heated, the strip will bend. Which metal will be on the outside of the curve? Why? (Hint: See Table 13–1.)

The bimetallic strips are generally employed in circuit breakers. It is strong and simple to operate, and inexpensive.

It can be used at higher temperatures and does not need any power source.

The coefficient of expansion for the aluminum is as follows:

\({\alpha _{{\rm{Al}}}} = 25 \times {10^{ - 6}}\;{\rm{^\circ }}{{\rm{C}}^{ - 1}}\) ... (i)

The coefficient of expansion for the iron is as follows:

\({\alpha _{{\rm{fe}}}} = 12 \times {10^{ - 6}}\;{\rm{^\circ }}{{\rm{C}}^{ - 1}}\) … (ii)

From the above equations (i) and (ii), it is clear that \({\alpha _{{\rm{Al}}}} > {\alpha _{{\rm{fe}}}}\). Thus, we can conclude that aluminum will expand more than iron for the same rise in temperature.

Hence, the bending curve will have aluminum metal on the outside and iron inside.