Bimetallic Strip, 4A30.10a
Topic and Concept:
Thermal Properties of Matter, 4A30. Solid Expansion
pira200 Listed
Location:
Cabinet: Thermodynamics Cabinet
Bay: (A3)
Shelf: #1
Abstract:
A bimetal strip of brass and steel is heated in a Bunsen burner flame and then cooled with liquid nitrogen.
Equipment |
Location |
ID Number |
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Bimetallic Strip |
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Burner |
location |
NA |
Liquid nitrogen |
location |
NA |
Safety glove and glasses |
location |
NA |
Rooms 2103, 2241, (and 2223 upon request) |
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Important Setup Notes:
This demonstration requires a supply of methane gas usually provided by the red and white gas carts found in rooms 2103, 2241, (and 2223 upon request).
- This demonstration requires a supply of liquid nitrogen. The main supply is located at the loading dock. If 12 hours notice given to lecture demo, supply will be provided.
Setup and Procedure:
To light the burner, connect the attached gas hose to the gas out (red panel) on the red and white gas cart.
- Open the gas valve.
- Light a match and bring it near the top of the burner.
- The flame will ignite the gas. Adjust the flame height accordingly by adjusting the valve.
- Heat the strip in the flame and watch as it bends toward the stainless steel side.
- Turn of the flame by closing the gas valve.
- Dip the strip into the liquid nitrogen and watch as the strip bends toward the brass side.
Cautions, Warnings, or Safety Concerns:
- Always use the gloves and safety glasses throughout this demonstration.
- Beware of the heated plate - contact with skin could cause severe burns!
- Use care when working with the liquid nitrogen - prolonged contact with skin causes severe frostbite!
Discussion:
The bimetallic strip consists of brass and stainless steel. Since brass has a higher coefficient of thermal expansion than stainless steel, it expands more for a given change in temperature than does the stainless steel side. Thus, when heated, the strip bends to the stainless steel side. On the other hand, when the strip is placed in liquid nitrogen (77K), the brass contracts more for a given change in temperature than does the stainless steel causing the strip to bend in the opposite direction.
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