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Theory:

We have learnt that if a body gains some electrons, it becomes negatively charged, and if a body loses some electrons, it becomes a positively charged body.
 
What happens if a charged body comes into contact with a conductor?
 
A conductor is a material which allows an electric charge to pass through it. So, when we touch a conductor (uncharged metal body) with a charged body, then the charges will spread evenly on the surface of the conductor. This method of transfer of charge is called conduction.
 
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Charging by conduction
 
How to find whether a body is charged or uncharged?
 
We can find whether a body is charged or uncharged by using a device called an electroscope.
 
Structure and working of electroscopes:
  • Gold and silver are mostly preferred to construct an electroscope because they are good conductors of electricity. If not, copper and aluminium can also be used.
  • Electroscopes consists of two closely placed metallic aluminium foils or strips.
  • The ends of the aluminium foils are attached to a metallic wire or rod. This whole hyphenated is kept in a glass bottle or glass jar since glass is a bad conductor.
  • When a charged body comes into contact with the metallic wire, then the charges will spread uniformly on the aluminium foils.
  • When the strips or aluminium foils are charged with similar charges, they repel each other and the aluminium foils become wide on, and it confirms the presence of charge on a body.
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Transfer of charges
  • If we touch the charged aluminium foil with our hands, then the charges pass through our bodies since human bodies are also a good conductor of charges. Finally, the charges get grounded to the earth.
  • The method of transferring charge from a charged object to the earth is called earthing.
  • In buildings, earthing is provided to protect us from electrical shocks due to any leakage of electrical current.
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