Introduction:
A bimetallic strip is composed of two different metals, M1 and M2, bonded together. It is designed to bend when exposed to temperature changes due to the different expansion rates of the two metals. In this case, M1 contracts more than M2 when cooled.

When the strip is heated:
When the bimetallic strip is heated, the two metals expand at different rates due to their different coefficients of linear expansion. The metal with the higher coefficient of linear expansion (M1) will expand more than the metal with the lower coefficient of linear expansion (M2). This differential expansion causes the bimetallic strip to bend.

Explanation:
Here is a detailed explanation of what happens when the bimetallic strip is heated:

1. Expansion of M1 and M2:
- When the strip is heated, both M1 and M2 expand.
- However, M1, which has a higher coefficient of linear expansion, will expand more than M2.
- This is because the coefficient of linear expansion is a measure of how much a material expands per unit length for each degree increase in temperature. A higher coefficient means a greater expansion for the same temperature change.

2. Differential expansion:
- Due to the differential expansion of M1 and M2, the bimetallic strip will bend.
- Since M1 expands more than M2, it will exert a greater force on the strip, causing it to curve towards the side of M2.
- This bending is a result of the different expansion rates of the two metals.

3. Curvature of the strip:
- As the bimetallic strip bends, the side with M1 will be in tension, while the side with M2 will be in compression.
- The tension in M1 and compression in M2 occur due to the differing expansion rates of the two metals.
- This curvature allows the bimetallic strip to be used in various applications, such as thermostats and temperature-sensitive switches.

Conclusion:
When the bimetallic strip is heated, the metal with the higher coefficient of linear expansion (M1) expands more than the metal with the lower coefficient of linear expansion (M2). This differential expansion causes the strip to bend, with the side of M1 in tension and the side of M2 in compression. Understanding the behavior of bimetallic strips allows for their use in various devices that rely on their bending properties in response to temperature changes.

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