Electrostatic induction

Electrostatic induction is the process by which a conductor becomes charged through the mere proximity of a charged object, without the two ever touching. When a charged rod is brought close to (but not touching) a neutral conductor, the free charges inside the conductor redistribute in response to the rod's field: charge of opposite sign to the rod is drawn to the side of the conductor nearer the rod, while charge of the same sign as the rod is pushed toward the far side, even though the conductor's total charge remains exactly zero throughout this stage. If the conductor is then briefly connected to the earth (grounded) while the charged rod is still held nearby, the like charge on the far side, being repelled by the rod, flows away to the earth, leaving only the unlike (attracted) charge on the conductor. Breaking the ground connection first, and only then removing the inducing rod, traps this induced charge permanently on the conductor -- which now carries a net charge exactly opposite in sign to the original rod, even though the rod and the conductor never made physical contact. This process, called …