Charging by Conduction and Induction

A conductor is full of electrons that can move freely. Touch a charged rod to a neutral metal sphere and some of that charge flows onto the sphere until both objects reach the same potential; if the two conductors are identical in size and shape, the total charge splits evenly between them. That's conduction: charge moves by direct contact, and the sphere ends up with the same sign as the rod.

Induction never touches the rod to the sphere. Bring a negative rod close to a neutral sphere, and its field pushes the sphere's free electrons to the far side without pulling any off. Ground the near side with a wire while the rod stays in place, and those repelled electrons have somewhere to escape to — they flow down the wire into the earth. Cut the ground connection first, still with the rod present, and the sphere is now short on electrons. Pull the rod away and that missing-electron sphere is left with a net positive charge, opposite the rod. If you pulled the rod away before grounding, everything would rush back and the sphere would return to neutral — the order of steps is what locks the charge in place.

Both processes matter because real circuits and capacitors depend on moving charge onto conductors without always having a battery or direct contact available. Conduction previews the idea that touching conductors reach a common potential, which comes back when you study capacitors sharing charge. Induction's trick of separating charge with a field, then grounding to make the separation permanent, is the same logic behind how a charged object can polarize and attract neutral matter even before Gauss's law gives you the tools to compute fields precisely.