A conductor contains mobile charge that can redistribute when an external electric field is applied. This makes it possible to rearrange charge—and even leave a conductor with net charge—without touching it with the charged source.

This process is called electrostatic induction.

Charge separation in a neutral conductor

Begin with an isolated neutral conductor. Bring a positively charged object nearby without contact.

The external electric field pushes mobile electrons in the conductor toward the nearby side. The near surface becomes negatively charged, while the far surface is left with an equal positive deficit.

The conductor is still neutral overall:

$$Q_{\rm conductor}=0.$$

Charge has been separated, not created.

If the external source is removed while the conductor remains isolated, the separated charges redistribute and the conductor returns to its original neutral state.

Leaving a net charge by grounding

A net charge can remain if the conductor is temporarily connected to a much larger charge reservoir such as Earth.

For a positive inducing charge:

1. bring the positive source near the initially neutral conductor;
2. while the source remains nearby, connect the conductor to ground;
3. electrons are attracted from ground into the conductor;
4. disconnect the ground before removing the inducing source;
5. remove the inducing source.

The extra electrons then spread over the isolated conductor, leaving it with net negative charge.

A negative inducing source produces the opposite result: electrons are repelled from the grounded conductor into Earth, so after the ground connection is removed the conductor is left positively charged.

Why the order matters

If the inducing source is removed while the conductor is still grounded, charge can simply flow between the conductor and Earth as the external field disappears. The intended net charge may not remain.

The sequence

$$\boxed{\text{source near}\rightarrow\text{ground}\rightarrow\text{remove ground}\rightarrow\text{remove source}}$$

is therefore essential for charging by induction.

Attraction of a neutral conductor

Even without grounding, a charged object can attract a neutral conductor. Suppose the source is positive. Negative induced charge accumulates on the nearer side and positive induced charge on the farther side.

Although the induced charges have equal magnitudes, the opposite charge is closer to the source and therefore experiences the stronger Coulomb interaction. The resulting force can be attractive.

This is why electrostatic attraction does not by itself prove that two objects carry opposite net charges: one object may be neutral but polarizable through mobile charge redistribution.

Induction versus conduction

Charging by conduction transfers charge through direct electrical contact with a charged body.

Charging by induction uses an external electric field to redistribute charge and, with grounding, can leave net charge without direct contact with the inducing source.

Both processes conserve total electric charge. The difference is the pathway by which charge is redistributed among the chosen objects and reservoirs.