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We are able to induce a positive charge on a metal putting an object highly negatively charged nearby. So, the positive charges on the metal will be attracted and the negative ones will be repelled. The negative charges will pass through the conducting cable to the ground, and positive charges will take their places on the metal. If the negatively charged object is still nearby when the wire is disconnected, the metal will be positively charged. Otherwise, the positive charges will be repelled and the metal will back to neutral charge.