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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