Charging by induction
Also called Induction charging
Charging by induction gives an object a net charge without ever touching it with a charged object. A nearby charge polarizes it, a ground connection lets charge escape, and breaking the ground first leaves a permanent charge opposite in sign to the inducing charge.
The procedure has four steps and the order is the whole point.
- Bring a charged object near a neutral conductor without contact. The conductor polarizes: like charge is pushed to the far side, opposite charge is drawn to the near side. Net charge so far, zero.
- Ground the conductor. Grounding means electrically connecting it to a much larger and approximately neutral system, such as Earth, which can absorb or supply charge freely. The charge repelled by the rod leaves through that connection.
- Break the ground connection while the charged object is still held in place. This is the step that makes the charge permanent.
- Remove the charged object. What is left redistributes over the conductor.
The object ends with a net charge opposite in sign to the inducing charge, and it was never touched. Contrast charging by contact or by friction, which transfers charge directly and leaves the object with the same sign as the charging object.
Reverse steps 3 and 4 and you undo the whole thing: the charge that had been pushed away simply returns through the ground. Without any ground connection you get induced charge separation and nothing more, which is real while the rod is near and gone once it leaves.
Charge is conserved at every step. The conductor's net charge changed only because charge was transferred between it and Earth.