Thermal Expansion of Metal Rods , 4A30.58

Topic and Concept:

• Thermal Properties of Matter, [:ThermalProperties#Thermometry: 4A30. Thermometry]

Location:

• Cabinet: [:ThermoCabinet:Thermodynamics (TD)]

• Bay: [:ThermoCabinetBayA3:(A3)]

• Shelf: #1

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Abstract:

This can also be called expansion rods. A metal blue box with various rods of different materials.

Important Setup Notes:

• This demonstration requires a supply of methane gas usually provided by the [:RedWhiteGasCarts: red and white gas carts] found in rooms 2103, 2241, (and 2223 upon request).

Setup and Procedure:

1. Choose a rod and place it on the holder.
2. Connect the burner to the methane supply.
3. Open the valve to let the gas flow, and light the burner using a match or lighter.
4. Place the flame under the rod to heat it.
5. Note the rate of expansion.
6. Turn of the gas by closing the valve, and allow some time for the rod to cool.
7. Carefully (using insulated gloves) switch out this rod for another one and repeat the heating process.
8. Note that the rate of expansion for this different material is different from the first rod.

Cautions, Warnings, or Safety Concerns:

• Beware of the heated rods - they can cause serious burns!
• Wear the safety grove and glasses.

Discussion:

• A given material of given length (1D), area (2D), or volume (3D) will have different geometric size at different temperatures. The equations describing this behavior is

  ΔL/L = α_L*ΔT (1D)

  ΔA/A = α_A*ΔT = α_L²*ΔT (2D)

  ΔV/V = α_V*ΔT = α_L³*ΔT (3D)

where L, A, and V are the initial length, area, and volume respectively when the material has temperature T_i. The Δ denotes the change in that quantity (final - initial). α_L, α_A, α_V are the linear, area, and volumetric coefficients of thermal expansion respectively. Note that for the 2D and 3D cases, equating α_A to α_L² and α_V to α_L³ is only valid for small expansions (or contractions) in isotropic materials.

This demonstration shows that different materials have different coefficients of thermal expansion. We have two different materials that start at room temperature and are heated to the temperature of the flame. Thus, ΔT is the same for all the rods You will see that the orange tip scale will move to the left at some rate. Then choose another rod in place of the previous one and heat it. The orange tip will move to the left at different rate.

our available materials with their respective linear thermal expansion coefficients in ascending order

Videos:

• [https://www.youtube.com/user/LectureDemostrations/videos?view=1 Lecture Demonstration's Youtube Channel]

References:

• [https://en.wikipedia.org/wiki/Thermal_expansion Wikipedia - Thermal Expansion]

• [http://en.wikipedia.org/wiki/Coefficient_of_thermal_expansion Wikipedia - Coefficient of Thermal Expansion]

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