[Virginia Tech Department of Physics]

Lecture Demonstrations

Heat & Thermodynamics
   

H14: Thermal Expansion of Metals

 

Purpose: To show the thermal expansion of metals, and how this effect is used in bimetallic thermometers and thermostats.

Description:

 

  1. Ball and ring. Ask the class whether the hole in the ring gets larger or smaller when heated. Show that the ball just fits through the ring. Heat the ball over the Bunsen burner until it will not go through the ring. While keeping the ball hot, heat the ring until the ball goes through.
  2. Bimetallic strip. Heat the strip with the heat gun or Bunsen burner and show that it bends due to differential expansion.
  3. Thermometer. Use the heat gun to heat the bimetallic strip of the thermometer and note the effect on the pointer.
  4. Thermostat. Plug in the apparatus and note that one bulb burns. Using the heat gun, heat the bimetallic strip until the light goes off, thus showing the effect of a thermostat to regulate a heating system. Additional heating bends the strip downward to the lower contact, lighting the other bulb. This shows the effect of a thermostat used to control a cooling system. CAUTION: THE BIMETALLIC STRIP CAN BE AT LINE VOLTAGE if the plug is inserted into its receptacle backwards. Whichever way the plug is inserted, SOME OF THE EXPOSED TERMINALS ARE AT LINE VOLTAGE.

Equipment List: Storage Location: CHEMP 130A
  Ball and ring on wooden handles C4.3
  Bimetallic strip on a wooden handle C4.3
  Model bimetallic thermometer C4.3
  Demonstration thermostat C4.3
  Heat gun H7
  Torch C4.4

References:

Manual: None   Setup Notes: H14 PIRA #:
Manufacturer(s): Other school's Demonstration web pages

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