A bimetallic strip consists of brass and iron when it is heated it bends into an arc with brass on the convex and iron on the concave side of the arc.  This happens because

Both the strips will expand in proportion to their linear thermal coefficients of expansion.
Coefficient of linear expansion of brass and iron are $19\times {10}^{-6} c^{-1}$
 and $12\times {10}^{-6}$$c^{-1}$ respectively. Hence, brass has a higher coefficient of linear expansion than iron.