A bimetallic strip is made of aluminum and steel (αₐₗᵤₘᵢₙᵢᵤₘ > αₛₜₑₑₗ) . On heating, the strip will

To understand how the bimetallic strip behaves when heated, we need to analyze the thermal expansion properties of the two metals involved.

A bimetallic strip consists of two different metal strips bonded together along their length. When the temperature of the strip changes, both metals expand or contract, but at different rates depending on their coefficient of linear expansion ($\alpha$).

The coefficient of linear expansion of aluminum is given as greater than that of steel:
${\alpha }_{\text{aluminum}}>{\alpha }_{\text{steel}}$
This means that for the same increase in temperature, aluminum will expand more in length than steel.

When the bimetallic strip is heated:
1. Aluminum tries to expand more and become longer than the steel strip.
2. Since the two strips are firmly bonded together, the aluminum strip cannot freely slide past the steel strip.
3. To accommodate the greater increase in length of aluminum while remaining bonded, the strip must bend into an arc.

In any bent or curved strip:
- The outer side of the curve (the convex side) has a larger radius and is longer.
- The inner side of the curve (the concave side) has a smaller radius and is shorter.

Since aluminum expands more and becomes longer, it must occupy the outer, convex side of the bend. Steel, expanding less and remaining shorter relative to aluminum, must occupy the inner, concave side of the bend.

Therefore, on heating, the strip will bend with the steel on the concave side.