Al Tobias (wat4y) - Office: Gibson S123 & Physics 218, (434) 924-0538
Physics Demo Manual
Demonstrations are cataloged according to PIRA Bibliography
PLEASE REQUEST DEMOS WELL IN ADVANCE
Due to Physics Building renovations, the lead time to set up demo requests has increased due to the need to transport equipment across campus. Please be kind and let me know well ahead of time what you need.
Choose a subtopic:
(Clicking a green button will add that demo to your list)
- Electric Fields And Potential
- Current and Resistance
- Electromotive Force And Current
- DC Circuits
- Magnetic Materials
- Complex Circuits
- Semiconductors And Tubes
- Transmission Lines and Antennas
video - Microwave Oven Experiments
To demonstrate the principle of operation, energy transfer etc. of microwaves using the microwave oven.
DEMO VIDEO DOWNLOAD w/ sound / 1920x1080 / 24.19Mb/s / 921MB size
DEMO VIDEO DOWNLOAD w/ sound / 854x480 / 5.69Mb/s / 218MB size
Since our microwave ovens are old donated units, some keypad numbers do not operate. As a workaround, use use another number on the touchpad to choose a time to run the oven.
Several experiments are available:
- COMPACT DISC (5 sec) - a CD placed in a microwave oven will spark brightly and get completely destroyed. Run oven for 5 seconds.
- LIGHT BULB (8 sec) - place a clear incandescent or fluorescent light bulb into a beaker partially filled with water (enough to immerse the metal socket connector), place in microwave and run oven for 8 seconds. The light bulb will glow brightly. Will explode if overheated.
- MICROWAVE PLASMA (10 sec) - light a match on a small cork stand, cover it up with a large beaker with two wood spacers on the bottom to allow air in, place inside oven and run oven for at least 9 seconds at a time. Very bright plasma balls will float at the ceiling of the dome. If plasma does not appear at first, run oven for an additional 10 seconds, right away!
- SMOOTH vs. SHARP METAL (5 sec) - metal objects can be placed in the microwave. Smooth object (such a ball bearing) will not spark, whereas, metal with many sharp points and thin material (such as aluminum foil) will heat up quickly at the sharp edges and spark/burn.
- MAGIC LIGHTS (5 sec) - one can use Magic Lights to check power settings and hot/cold spots inside oven space. Set a cup of water in the oven first, then place Magic Lights where you'll be able to see it thru the window. Description from the manufacturer: "Magic Lights is made from high-impact, acrylic plastic and special, proprietary, gas-filled lamps which provide long life and extremely bright light."
Reference: M. Vollmer, et. al. Microwave oven experiments with
metals and light sources, Phys. Ed. 39 (6).
The water is used to absorb some of the microwave energy the oven produces. These ovens are not designed to run with no "load". The klystron would heat up and burn out if not loaded properly.