Today, we spent quite an large amount on going through excercise 7. One of the main reasons were that it was because some of our classmates were not quite sure how bimetallic strips work and that the diagram given was quite vague. This caused some confusion among the students. So i decided to do a blog entry on bimetallic strips.
| Material | Expansion
Coefficient |
| Aluminium | 2.4 x 10-5 K-1 |
| Iron (steel) | 1.2 x 10-5 K-1 |
| Copper | 1.7 x 10-5 K-1 |
| Brass | 1.9 x 10-5 K-1 |
| Glass (pyrex) | 3.3 x 10-6 K-1 |
| Concrete | 1.2 x 10-5 K-1 |
| Invar | <1.3 x 10-6 K-1 |
| Table 1 |
|
| |
Volume Expansion of a Solid
The volume of a solid (including metals except for mercury) is
slightly dependent on temperature. Let the length L
o be the length of the solid when the temperature is T
o. When the temperature rises the length will change (for most solids the length will increase) Providing the temperature increase is not too great the length of the solid will change by an amount
| change in L = a * Lo * (T - To) |
where the constant
a is the thermal expansion coefficient, which accounts for the different solids that could possibly be used.
Uses for Bimetallic strips
Bimetallic strips are made in coils to increase their sensitivity for use in thermostats. One of the many uses for bimetallic strips is in electrical breakers where excessive current through the strip heats it and bends it to trip the switch to interrupt the current.
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