6.1 Conservation of Charge
The Van de Graaff Generator
How the Van de Graaff works is quite simple. Go to Virtual Lab: The Van de Graaff Generator with Podcast explains how the generator charges and how to discharge the generator as well.
In any isolated system, while charges may move and be transferred between objects the net charge will not change. This idea is known as the Law of Conservation of Charge. Furthermore, like charges experience forces of repulsion, while
unlike charges experience forces of attraction. This is known as the Law of Charges. These two laws are demonstrated in the following Quick Lab and the following Self-Check questions.
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The Law of Conservation of Charge The net charge of an isolated system is conserved |
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The Law of Charges |
Step 2: Bring the balloon between the wall and the sweater and let the balloon go. Note your observation.
Step 3: Bring the balloon close to the wall and note what happens.
Step 3: Switch to two balloons and push the "Reset Balloon" and "Remove Wall" button.
Step 4: Rub each balloon to the sweater just once.
Step 5: Drag one balloon to the left then drag the other close to the first balloon and observe what happens.
What happens when the balloon is rubbed on the sweater.
The balloon is attracted to the wool sweater because it has picked up electrons, giving the balloon a net negative charge and the wool sweater a net positive charge. Because opposite charges attract the balloon is attracted to the sweater.
Explain how the law of charges applies to the balloon and the sweater.
The balloon is attracted to the wool sweater because it has picked up electrons, giving the balloon a net negative charge and the wool sweater a net positive charge. The law of charges states that like charges repel and unlike charges attract therefore the balloon is attracted to the sweater.
What happens when you rub the two balloons on the sweater and try to make them touch?
Each balloon ends up having a net negative charge. The law of charges states that like charges repel and unlike charges attract therefore the force of repulsion pushes the balloons apart
Apply Newton's third law to the electrostatic forces that act on each balloon.
According to Newton's third law, the force exerted by the first balloon on the second balloon is equal but opposite to the force exerted by the second balloon on the first balloon. The equation looks like this:
Draw a free-body diagram to illustrate the forces acting on each balloon.
Fg = force due to gravity
Fe = electrostatic force
Ft = force of tension
