4B50.60: Greenhouse Effect

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Video: Watch this demo

Instructor’s video

Description: By using a computer and digital display thermometer, you can show the class that equilibrium temperature increases when the thermocouple is encased in a plastic bottle, and then increases again when water vapor (a greenhouse gas) is present inside the bottle.


  • Digital display multimeter (DVM), with thermocouple.
  • Computer with COM port to connect to DVM, DVM software installed, and an additional video output.
  • Plastic bottle with a small hole drilled in the cap.
  • Variac.
  • Overhead projector lamp, ready to mount on stand.
  • Three-legged stands (2).
  • S-clamp.
  • Pincer clamp.

Setup Procedure:

  1. Mount lamp to stand, and connect to variac. Plug variac into table.
  2. Thread the end of the thermocouple through the hole in the bottle cap; secure with tape.
  3. Mount the bottle cap and thermocouple in the pincer clamp; mount the combination on the other stand, so that the thermocouple is about 6 to 8 inches from the lamp.
  4. Connect thermocouple to DVM, and plug DVM into table.
  5. Connect DVM to computer.
  6. Boot computer and start DVM software.
  7. With DVM turned ON, make sure that the software is displaying a readout of the temperature!

Demonstration Procedure:

  1. Switch video projector to show the DVM-connected computer.
  2. Make sure the projector is showing the display of temperature that you want (number, or graph).
  3. If graphing press “start” to begin recording data.
  4. Turn on light, watch temperature increase to equilibrium, note equilibrium temperature.
  5. Screw bottle into cap so that the thermocouple is inside. Note new, higher equilibrium temperature.
  6. Remove bottle, add a little bit of water (a teaspoon or less should be sufficient), and replace. Notice an ever higher equilibrium temperature!