4A30.10 - Bimetallic Strip
Show how a simple bimetallic strip reacts to different temperatures.
Obtain demonstration equipment materials. Place bimetallic strip on Aluminum plate. Check that the propane torch works.
Turn on gas supply and ignite flame. Pick up the bimetallic strip and move it around in the flame. When the it gets hot, the metal will begin to bend in a direction. This is because of the difference in thermal expansion of brass and steel. Cool down the strip by placing it back on to the aluminum plate.
**Optional** - an alternative setup involving thermal contraction and liquid nitrogen (LN2) can be provided which shows bending in the opposite direction from heating. This option has additional safety requirements of gloves, goggles, cryogenic warning signs.
A piece of brass and steel, each with different coefficients of expansion, are stuck together in a single strip. When they are heated in a flame, the different expansion coefficients cause the strip to bend in a curve toward the one that expands less (steel). To get the strip to bend in the opposite direction, use liquid N2.