Let me discuss the other frequently used demonstration of charge being acquired: rubbing an inflated balloon against (long) hair. As the hair becomes charged the hairs tends to stand out, as there is electrostatic repulstion between the individual hairs. The hairs are attracted to the balloon. We notice that even when the hairs touch the balloon the charge isn't lost. This is explained as follows: the hair and the balloon are both very poor conductors of electricity. This means that any charge that has build up remains at the location where it was build up. The charge will not flow along the length of the hair, the charge will not flow along the surface of the balloon. The fact that both are poor conductors is part of the explanation why those substances can build up charge in the first place. When materials that are conductive are rubbed together you don't get buildup of charge because any minute buildup of charge just flows right back. Glass rod and silk Comparison with the hair and balloon setup: In glass rod and silk demonstrations what you can get to move is very tiny objects, such as very small pieces of paper. Any object that is heavier than those slivers of paper (or strands of hair) will not visibly move. There are devices that can build a large electrostatic charge, such as a van de Graaf generator. Such a device builds up charge over time by having a band run around in a loop, acquiring charge at one end and transferring charge to some accumulater at the other end. In the case of rubbing a glass rod and silk the amount of charge that you build up is not enough to visibly move the silk cloth. The cloth is dense and strongly connected. To see motion you would need to unravel the strands of the cloth in loose fibers.
When silk is rubbed on a glass rod, an electrostatic charge is generated in a phenomenon known as the triboelectric effect. It is this electric charge that gives you a shock in winter when your rubber-soled shoes rub against a carpeted floor. The triboelectric series is a list of materials sorted according to their electrostatic behavior; using the list, you can predict the electrostatic effects when silk is rubbed on a glass rod.
The triboelectric series starts at the top with materials that strongly acquire a positive electric charge; the list continues down with materials becoming more negative. This occurs because some materials will lose electrons to other materials when they come in contact. When you rub two items together, the materials closer to the top of the series lose electrons and take on a positive charge; the materials lower on the series gain electrons and become negatively charged.
Because glass is closer to the top of the triboelectric series than silk, it develops a positive charge; silk becomes just as strongly charged, but the sign of the charge is negative. If you rub the two materials together, then touch the glass rod to two small bits of styrofoam, both pieces of styrofoam will lose electrons to the glass rod, become positively charged and will repel each other, because like charges repel. If you touch the rod to one piece of styrofoam and the silk to the other piece, the former piece will lose electrons take on a positive charge and the latter piece will gain electrons and take on a negative charge. The opposite charges will cause the pieces to attract. Uh-Oh! That’s all you get for now. We would love to personalise your learning journey. Sign Up to explore more. Sign Up or Login Skip for now Uh-Oh! That’s all you get for now. We would love to personalise your learning journey. Sign Up to explore more. Sign Up or Login Skip for now |
When a glass rod is rubbed against silk the silk becomes?
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