A bimetal plate consists of two materials of different coefficients of thermal expansion. The coefficient of thermal expansion of the top part of the plate is less than the bottom part. If the temperature of the entire plate increases, what happens to the plate?

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Question restated: A bimetal plate consists of two materials of different coefficients of thermal expansion. The coefficient of thermal expansion of the top part of the plate is less than the bottom part. If the temperature of the entire plate increases, what happens to the plate?

Answer options:
- Bends up
- Bends down
- Contracts
- Stays the same

Analysis of each option:
- Option: Bends up
This outcome aligns with the basic behavior of a bimetallic strip when heated: the layer with the larger coefficient of thermal expansion (the bottom part in this case) wants to lengthen more than the top layer. Since the two layers are bonded, the strip cannot lengthen uniformly, so it must bend. The layer with the greater expansion becomes the outer, longer side of the bend, while the layer with the smaller expansion forms the inner side. Because the bottom expands more and the top expands less, the curvature is such that the free end moves upward, i.e., bends up.

- Option: Bends down
If this were true, it would imply the top layer (the one with the smaller expansion) ends up on the outside of the bend or otherwise causes the whole plate to curve in the opposite vertical direction. That would require the top layer to be the expanding side or the geometry to force the outer arc to be on the top, which contradicts the principle that the larger expansion tends to be the outer arc.

- Option: Contracts
Thermal contraction would occur if the temperature decreased or if both materials had unusual behavior reversing the usual expansion trend. However, the problem states the temperature increases and uses standard positive coefficients of thermal expansion, so overall contraction is not expected.

- Option: Stays the same
Staying the same would require equal expansions in both layers or a perfectly rigid connection with zero bending. Since the top and bottom have different expansion coefficients and are bonded, there is a differential strain that must be accommodated by bending, so this option does not reflect the described scenario.

Summary: The key concept is that the layer with the larger coefficient of thermal expansion expands more with temperature, causing the plate to bend toward the layer with the smaller expansion. Given the top part has the smaller coefficient, the plate bends in the direction described by the top side becoming the inner radius, which corresponds to bending up in the depicted orientation.

SPHY001 Practice Quiz - Unit 13 | LA053

A bimetal plate consists of two materials of different coefficients of thermal expansion. The coefficient of thermal expansion of the top part of the plate is less than the bottom part. If the temperature of the entire plate increases, what happens to the plate?

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