Just inside the front of a television screen there is a positively charges surface. (We'll learn about the details of how a television works later this semester.)
1. The front of a television screen tends to get dusty over time. Briefly explain how a neutral (no net charge) dust particle can be attracted to the front of the positively charged screen.
2. If you rub a balloon in your hair it will become negatively charged. If you then dangle the balloon from a string in front of the television screen, what will happen to the balloon?
3. For the above question, how does the force on the balloon vary with its distance from the television screen? Please give a descriptive answer, not a formula or equation.
4. After rubbing the balloon in your hair, your hair may stand on end as separated strands. Briefly explain this behavior. This works particularly well if you hair is very dry so that it acts as a good insulator.
5. Suppose you have two televisions and are curious which one has a larger charge on the front of its screen. To find out you place the two televisions with their screens facing each other and just a few inches apart. You then rub a piece of yarn against a balloon to give the yarn a positive charge. You stand beside the two televisions so that one is on your left and the other is on your right and dangle the charged yarn in between the two. The yarn is attracted toward the screen on your right. Which television screen has more positive charge on its front face?
6. For the above situation, in which direction does the electric field point?
A xerographic copier can be used to copy onto clear plastic sheets such as those used with an overhead transparency projector. In many copiers, the plastic comes out with lots of positive charge on one side and lots of negative charge on the other.
7. Plastic is a good insulator. At what energy is the Fermi level located in plastic?
8. If you hold a piece of plastic that has just come out of the copier under an incandescent lamp which produces lots of visible light, will the charges migrate from one side of the plastic to the other leaving the page unpolarized? Explain why.