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Static Electricity |
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Static electricity was known to people more than 2500 years ago. The Greeks knew about the attractive property of the resin amber. They knew that by rubbing amber with cloth, it could be made to attract small feathers. The Greek name for amber was 'elektron'. |
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Two Kinds of Electric Charges |
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You can electrify a glass rod by rubbing it with silk. Suspend such an electrified rod by a silk thread as shown in figure. If you bring another glass rod electrified in the same manner, you will notice that the rods repel each other. |
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Atomic Structure and Charges |
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The existence of negative and positive charges on these materials can be explained on the basis of the structure of the atom. Almost all the mass of an atom resides in a central nucleus which contains a number of tightly packed protons and neutrons. |
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Conductors and Insulators |
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In case of certain materials like glass, the electrons are firmly 'bound' to the atoms and they do not normally move. Such materials are known as the 'insulators' or bad conductors of electricity. Polythene, ebonite, silk, fur, plastic etc. belong to this category. The charge produced by rubbing a glass does not flow away, because it is an insulator. These charges are called static because they do not move. |
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Charging by Friction |
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Keeping in mind the structure of the atom, we can easily explain charging by rubbing. When glass rod is rubbed with silk, some of the electrons from the atoms on glass are transferred to silk. Because there is a deficiency of electrons in the glass, it becomes positively charged. On the other hand, as the silk has acquired additional electrons it becomes negatively charged. |
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Electroscope |
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When a charged body is brought near the electroscope the light weight pith ball is first attracted to the rod. Once it has touched the rod it gets repelled. When the pith ball comes in contact with the rod some of the charge from the rod gets transferred to the pith ball. As a result, it acquires similar charge. Because of the similar charge it then gets repelled. Attraction precedes repulsion. |
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Charging by Conduction and by Induction |
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It should always be remembered that whenever you have to charge a body, it must be insulated from the earth. It means that the body should be supported on a stand which is made of an insulating material which does not allow charges to pass into the earth. |
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Explanation of Induction |
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When the positively charged body is brought near the two cans A and B, the electrons (-ve charges) from both the cans are attracted and get concentrated on B which is near R. |
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Uses of Gold leaf Electroscope |
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To detect a charge on a rod 'A' or 'B' bring the rod near to the metallic disc or cap of the electroscope. In either case the leaf diverges as shown in the diagram. |
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Lightning and Lightning Conductors |
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During thunderstorms, large amount of electrical charge separation takes place in the clouds. As a result, some regions of the cloud have overall positive charge, while others have overall negative charge. |
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Photocopier |
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Then term 'Xerography'; the use of Photoelectric phenomena to transfer an image from one sheet of paper to another comes from the Greek words for "dry" and "writing". |
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Current Electricity |
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One of the greatest discoveries of the eighteenth century was the discovery of electricity. Think of life today without electricity and you will realize the part electricity plays in our day to day life. |
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Electric Circuits |
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Your everyday experiences have familiarised you with many electric circuits. Let us take an example of an electric circuit with a battery (a source of electricity), toaster and a switch. |
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Source of Electricity |
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Electrons in different metals can have different energies. If two of these metals are placed in a conducting liquid (electrolyte) a difference in electrical potential is set up between them. A pair of different metals arranged in this way is an electrochemical cell. It converts chemical energy to electrical energy. These cells are known as Primary Cells. |
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Summary |
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When substances like glass and silk or ebonite and fur are rubbed, positive and negative charges of equal amount are simultaneously produced. |
