# Bimetallic Spiral Thermometer

Bimetallic Spiral Thermometer

This Demonstration simulates a classical bimetallic spiral thermometer (dial or coil thermometer).

An Archimedes's spiral made of a coiled bimetal strip gives a deflection proportional to the surrounding temperature and can serve as a thermometer.

The angular deflection of a bimetal spiral of length and strip thickness is given by , where and are the coefficients of linear expansion of the component materials used.

L

s

ϕ=(-)(T-)L/s

α

1

α

2

T

0

α

1

α

2