A bimetallic strip consists of brass and iron strips welded together. It is mounted rigidly of the base as shown. The strip is then heated. The bimetal strip (consider ${\alpha }_{brass}>{\alpha }_{iron}$)

So strip bends towards left  ${\alpha }_{brass}=19\times {{10}^{-6}}^0{C}^{-1};{\alpha }_{iron}=12\times {{10}^{-6}}^0{C}^{-1}$

We known when, bimetallic strip heated it bends such that metal with higher $\alpha$  comes on to convex side and metal with lower  $\alpha$  on concave side. ${\alpha }_{brass}>{\alpha }_{iron}$