Force Between Charges
Force Between Charges
The force exerted by non-moving (static) charges on each other is called the electrostatic force. The electrostatic force between:
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like charges is repulsive
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opposite (unlike) charges is attractive.
In other words, like charges repel each other while opposite charges attract each other.
The closer together the charges are, the stronger the electrostatic force between them.
Did You Know?
The word “electron” comes from the Greek word for amber. The ancient Greeks observed that if you rubbed a piece of amber, you could use it to pick up bits of straw.
Example: Application of Electrostatic Forces
Question
Two charged metal spheres hang from strings and are free to move as shown in the picture below. The right hand sphere is positively charged. The charge on the left hand sphere is unknown.
The left sphere is now brought close to the right sphere.
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If the left hand sphere swings towards the right hand sphere, what can you say about the charge on the left sphere and why?
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If the left hand sphere swings away from the right hand sphere, what can you say about the charge on the left sphere and why?
Step 1: Analyse the problem
In the first case, we have a sphere with positive charge which is attracting the left charged sphere. We need to find the charge on the left sphere.
Step 2: Identify the principles
We are dealing with electrostatic forces between charged objects. Therefore, we know that like charges repel each other and opposite charges attract each other.
Step 3: Apply the principles
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In the first case, the positively charged sphere is attracting the left sphere. Since an electrostatic force between unlike charges is attractive, the left sphere must be negatively charged.
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In the second case, the positively charged sphere repels the left sphere. Like charges repel each other. Therefore, the left sphere must now also be positively charged.
This lesson is part of:
Electric Charges and Fields