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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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| Repeat the experiment using two ebonite rods rubbed with fur. They will also be found to repel one another. |
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| Now suspend an ebonite rod rubbed with fur and bring the end of a glass rod rubbed with silk. You will notice that instead of repelling each other, the two will attract one another. |
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| What conclusions can we draw from these observations? |
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 Glass rod and ebonite rod get charged during the process of rubbing. |
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When the charges are similar, they repel each other. |
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| (Remember what happened when the two glass rods rubbed with silk and the two ebonite rods rubbed with fur were brought near each other). |
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When the charges are not similar they attract each other. |
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| (When the charged glass rod is brought near a charged ebonite rod, both the rods attract each other.) |
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| Thus like charges repel one another but unlike attract one another. This is known as law of electrostatics. |
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| Early investigators decided to call the charge on ebonite rubbed with fur, a negative (-ve) charge. As the charge on a glass rod rubbed with silk was found to be a different type it was called a positive (+ve) charge. Since like charges repel, two positive or two negative charges repel each other. On the other hand, as the unlike charges attract, a negative and a positive charge attract each other. |
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| The charge on rubbed polythene is a negative charge. The charge on a rubbed acetate strip is a positive charge. |
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