When a bimetallic strip is heated, it
A) Does not bend at all
B) Gets twisted in the form of a helix
C) Bend in the form of an arc with the more expandable metal outside
D) Bend in the form of an arc with the more expandable metal inside

Hint: A bimetallic strip is used to convert a temperature change into mechanical displacement due to expansion of dimensions due to heat. The strip consists of two strips of different metals which expand at different rates as they are heated.

Complete step by step answer:
Every metallic material in the universe has its own sets of properties like electrical property, mechanical property, thermal properties, etc. A bimetallic strip works on the principle of thermal expansion due to a change in temperature or more specifically expansion due to an increase in temperature. There will be a change in the volume of metal with the temperature change. The bimetallic strip works on two behaviours of metal:
1) When the metal is heated, it expands due to the extra thermal energy
2) Different metals expand at different rates due to different thermal properties.
When the strip is heated, the more expandable metal which is the metal with a higher expansion rate will expand more than the other metal for the same difference in temperature. The result of this behaviour will be that the strip will deform in the form of an arc such that the more expandable metal is outside since it will have a higher length due to the temperature increase than the metal on the inside.

Therefore, option (C) is correct.

Note: Bimetallic strips are specifically used for this behaviour that we described above. Their action can be thought of as converting thermal energy into mechanical energy. They are used in measuring temperatures by measuring the relative curvature of the strip when heated or cooled.