A bimetallic strip consists of metals $$A$$ and $$B$$. It is mounted rigidly as shown. The metal $$A$$ has higher coefficient of expansion compared to that of metal $$B$$. When the bimetallic strip is placed in a cold bath, it will:

We need to determine what happens to a bimetallic strip made of metals $$A$$ and $$B$$ when it is placed in a cold bath, given that metal $$A$$ has a higher coefficient of linear expansion ($$\alpha_A > \alpha_B$$) than metal $$B$$.

1. Understanding Thermal Expansion and Contraction

The change in length ($$\Delta L$$) of a metallic rod due to a change in temperature ($$\Delta T$$) is governed by the formula:

$$\Delta L = L_0 \alpha \Delta T$$

Where:

• $$L_0$$ is the initial length.
• $$\alpha$$ is the coefficient of linear expansion.
• $$\Delta T$$ is the change in temperature.

2. Behavior in a Cold Bath (Cooling Phase)

When the strip is placed in a cold bath, the temperature decreases ($$\Delta T < 0$$), causing both metals to contract (shrink).

• Since metal $$A$$ has a higher coefficient of expansion ($$\alpha_A > \alpha_B$$), it is more sensitive to temperature variations.
• This means that upon cooling, metal $$A$$ will contract more (become shorter) than metal $$B$$.

3. Direction of Bending

Because the two metals are bonded together rigidly, they cannot slide past one another. To accommodate the unequal shortening while remaining joined:

• The metal that contracts more (metal $$A$$) must form the inner curve of the bend.
• The metal that contracts less (metal $$B$$) must form the outer curve of the bend.

Based on the standard mounting arrangement where metal $$A$$ is placed on the left and metal $$B$$ is placed on the right, metal $$A$$ shortening more forces the strip to curve inward toward its own side.

Therefore, the bimetallic strip will bend towards the left.

Correct Answer: Option D: Bend towards the left