I preformed the following experiments in my microwave oven recently. I took a sheet of paper and drew a very heavy line on it with a pencil. The line was about 1/8 inch wide and 1-1/2 inches long. Pencil lead is mostly graphite, which can conduct electricity, but not very well.
1. First I placed the paper in the microwave with the line oriented vertically, propped up against a mug of water. The line was near the center of the microwave oven. When I turned on the oven, the paper behind the line caught fire almost immediately. Briefly explain why.
2. Next, I placed a second piece of paper in the oven with a line in the same location, but oriented horizontally. This time the paper did not catch fire even after several minutes with the oven on. What is the polarization of the microwave field in this region of the oven (in what direction is the electric field oscillating)?
3. I then rotated the piece of paper so that the line was again oriented vertically, but moved it a few inches to one side of the initial location. The paper did not catch fire even after the oven had been on for several minutes. If I assume that the polarization of the microwave field is the same at this location then I might conclude that the strength of the field is less here. Describe how the microwave field can be strong in one location, but weak in another.
4. Finally, I drew a heavy line about 1/8 inch wide and 1/2 inch long on a piece of paper and placed it in the middle of the oven (in the same location as question 1 and oriented vertically). The paper did not catch fire even after several minutes with the microwave on. Explain how the length of the line can effect how the microwave field couples to it.
You are on a camping trip with some friends and, having just seen "The Blair Witch Project," someone suggests telling ghost stories in the evening. You sit in a circle inside the tent and the first storyteller shines a flashlight in her face to cast eerie shadows across its features.
5. As the light shines in her face some of it falls onto the diamond stud piercing her nose, casting a brilliant display of colors across the ceiling of the tent. Explain how the light from the flashlight is separated into this rainbow of colors.
6. In addition to the colored spots on the tent ceiling, there are bright white spots. These are reflections from the front of each of the facets of the diamond stud. Explain why some light is reflected from these surfaces.
7. The story continues and the flashlight begins to glow dimly as the batteries wear out. The colored spots on the ceiling of the tent no longer contain all of the colors of the rainbow. Which colors are missing?
8. How do the current through and voltage across the dimly glowing bulb compare to when it was glowing brightly?