CBSE Class 10 Answered

Yes, nucleus do hold back the electron in shells, but electron in the farthest shell are not influenced so much by the attraction of protons in the nucleus. So if an external potential, something that'll line up all the available free electrons from all the atoms together and make them move, they'll move and this constitutes an electric current. Electrons are not lost, they are just like the water which might be circulating in a circular connection of pipes, propelled by a pump.

A battery does the job of a pump in an electric circuit.

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