Charging by Induction - Questions 8 Help

Charging by induction is a charging process in which a charged object is brought near to a neutral object. The neutral object becomes polarized. The neutral object is then touched by a ground, This touching to the ground forces a movement of electrons between the neutral object and the ground. When the ground is pulled away, the neutral object is permanently charged.

This charging by induction process occurs in two steps. The first step is referred to as the polarization step. When the negatively-charged balloon is held near neutral sphere A, there is a separation of the positive charges from the negative charges within the sphere. The second step is the charging step. When sphere A is touched by sphere B, it becomes charged. You must be able to explain each step in terms of the movement of particles within the objects. Details about each step are described below.

Polarization Step
During the polarization step, the presence of the negatively-charged balloon forces (or induces) a movement of electrons within the metal sphere A. Knowing which way electrons move within sphere A is based on the two fundamental rules of charge interactions:

• Oppositely-charged objects attract.
• Like-charged objects repel.

Since the electrons and the negatively-charged balloon are like-charged, the electrons in sphere A will move away from the balloon.

What about the protons? Don't they move? No! Protons are located in the nucleus of atoms. They are tightly bound in the nucleus. The nucleus would have to be split open in order for the protons to escape the nucleus. Atom-splitting just doesn't happen when you bring a charged object near a neutral object.

Why don't electrons move from the balloon onto metal sphere A? Electrons are free to move within conducting materials. Sphere A is made of metal - a conductor. This allows the electrons to move from one location on sphere A to another location. But air separates sphere A from the balloon. Air is not a good conductor; it prevents the electrons from moving through it. The result is that the electrons do not move from the balloon to sphere A.

The polarization step polarizes the charges in sphere A. The mass migration of electrons from the left side of sphere A to the right side of sphere A leaves the right side with an overall negative charge and the left side with an overall positive charge. Yet because there has been no movement of electrons onto or off of sphere A, it is still neutral. The charging doesn't occur until the next step.


Charging Step
When sphere A is touched by sphere B, there is a movement of electrons from sphere A to sphere B. This electron movement is induced by the presence of the negatively-charged balloon. Electrons, being negatively-charged, are repelled by negatively-charged objects like the balloon. So the action of touching sphere B to sphere A results in the movement of electrons into sphere B. This is a charging step. Because electrons leave sphere A, sphere A becomes positively charged.

But what about the protons? Don't protons move during this step? No! As discussed above, protons are tightly bound in the nucleus of atoms. They are unable to move during electrostatic experiments. Charging processes are always explained in terms of electron movement.