Thermodynamics
4B50.60: Greenhouse Effect
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.
Equipment:
- 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:
- Mount lamp to stand, and connect to variac. Plug variac into table.
- Thread the end of the thermocouple through the hole in the bottle cap; secure with tape.
- 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.
- Connect thermocouple to DVM, and plug DVM into table.
- Connect DVM to computer.
- Boot computer and start DVM software.
- With DVM turned ON, make sure that the software is displaying a readout of the temperature!
Demonstration Procedure:
- Switch video projector to show the DVM-connected computer.
- Make sure the projector is showing the display of temperature that you want (number, or graph).
- If graphing press "start" to begin recording data.
- Turn on light, watch temperature increase to equilibrium, note equilibrium temperature.
- Screw bottle into cap so that the thermocouple is inside. Note new, higher equilibrium temperature.
- Remove bottle, add a little bit of water (a teaspoon or less should be sufficient), and replace. Notice an ever higher equilibrium temperature!
Note:
Back