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| Electric Charge |
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| It is very difficult to define, what an electric charge is? |
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| The word 'electric' is derived from the Greek word 'elektron' meaning amber. The existence of charges were known when charged particles were produced by rubbing (due to friction) of suitable materials. These facts are demonstrated by simple experiments. |
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| (a) Suspend a glass rod rubbed with silk. Bring another glass rod rubbed with silk nearer to the suspended rod. It is observed that ,the suspended rod will swing away, showing repulsion. |
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| (b) Similarly, suspend a plastic rod rubbed with fur and bring another plastic rod rubbed with fur closer to it, we observe that the rods repel . |
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| (c) Again, if we suspend a glass rod rubbed with silk and bring a plastic rod rubbed with fur nearer to the glass rod, we observe that the rods attract. |
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| From the above, we find that glass rod rubbed with silk acquire 'something' different from that of plastic rubbed with fur. That 'something' is called 'charge'. |
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| By convention, the charge on the glass rod when rubbed with silk is positive and the charge on the plastic rod when rubbed with fur is negative. It is due to mechanical friction that the electrons are torn from the atoms. |
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