Bimetallic Strip and Ball and Ring Experiment

Heating Metal

Two metals with different coefficients of thermal expansion are welded together to make the bimetallic strip. When heated, the strip curls, because one metal expands more than the other. When coiled like in a thermostat, the coil unwinds (expands with heat) or tightens (contracts with less heat). This causes a pointer to move across a dial.

Application: The bimetallic strip is used as a thermostat switch for temperature control. A bimetallic strip using brass and iron, the brass expands more than iron.

Top of dial sets the desired temp. Bottom of dial measures actual room temp.

Top of dial sets the desired temp. Bottom of dial measures actual room temp.

The glass vial is tilted by the expanding bimetallic coil

the fingers mesh together in the summer due to thermal expansion

Conventional Thermostats
A bi-metal coil contracts when "cold" and expands when warm. The sensor's movement trips a switch to "On" or "Off." The switch may be a mercury-activated switch with mercury in a glass vial that completes or breaks an electrical circuit when the vial is tilted by the coil.

Thermal Expansion - Ball & Ring:
When both ball and ring are at room temperature (20 °C), the ball fits through the ring. When the ball is heated, it no longer fits.

SCIENCE EXPERIMENT WRITE UP

Purpose:

Hypothesis: What do you think will happen? What are you trying to prove or disprove?

Materials:

Steps:

Pre-Observations:

Observations: (Include Before / After Labelled Diagrams) - descriptions, measurable changes.

Conclusion: (What did you learn? - Prove or disprove?)

Real World Application: How do we apply this knowledge to the real world? How do we put this science to use? How does this (technology / discovery / concept) help people?