Charging by Induction

Have you ever been able to stick a balloon onto a wall after rubbing it on your sweater? How is this possible? You know that the balloon gains a static charge because of the rubbing. You also know that opposite charges attract each other. However, the wall is neutral. How does the balloon stick to it?

Induced Charged Separation Rubbing a balloon against your sweater makes it negative. The wall is neutral (+ve = -ve) Bringing the –ve balloon close to the wall will cause the electrons in the balloon to repel the electrons in the wall. This is known as induced charge separation.

Figure 1 shows how induced charge separation allows a negatively charge balloon to stick to a neutral wall.

Induced charge separation leaves a +ve charge on the surface of the wall. This temporary charge is an example of charging by induction. A portion of the neutral object (the wall) was charged by brining another charged object (the balloon) close to it.

Grounding You can return any charged object to neutral by adding or removing electrons. Large objects like the Earth can gain or lose electrons and remain neutral because the charges are spread over a huge area. The process of removing charges from objects by contact with a large, neutral object is called grounding. Figure 3.

So, Why the Shock? As you walk across the carpet, your socks and the carpet rub together giving your socks – and you – a negative charge – Charging by friction The metal door knob is a conductor – electrons can move easily inside it As your hand approaches the door knob, the electrons “jump” to it – Grounding via the doorknob