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A positively charged rod is brought near the cap of a leaf electroscope. The cap is then earthed momentarily by touching with the finger. Finally the rod is withdrawn. The electroscope is found to be negatively charged. Explain how this charge is acquired.

Answer Text:
The positive rod attracts the negative charge to the cap and repels the positive charge to the leaf. On earthing, the positive charge is neutralized and when the rod is withdrawn the negative charge on the cap repels each other and redistributes making the electroscope negatively charged