The diagram shows a bimetallic strip used as a thermostat in a circuit. The copper expands more than the invar for the same temperature rise. What will be switched on when the bimetallic strip becomes hot?

Since copper expands more than invar , therefore side of copper will become convex and side of invar will become concave therefore bimetallic strip will bend upwards and upward circuit will be short and therefore bell and lamp will turn on.