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Question Video: Separating Positive and Negative Charges Science

The picture shows a positive charge and a negative charge that are near each other. The charges are fixed in place and cannot move. Complete the following sentence: The separation of the positive and negative charges creates an _ between them.

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Video Transcript

The picture shows a positive charge and a negative charge that are near each other. The charges are fixed in place and cannot move. Complete the following sentence. The separation of the positive and negative charges creates an (A) electric current or (B) electric potential difference between them.

In this question, we are asked to decide when there are two charges, one positive and the other negative, fixed at a small distance apart, whether there is an electric current or an electric potential difference between them. We know that two opposite charges produce forces that attract each other. The force that acts on either charge is towards the other charge. Recall that an electric current is defined as the motion of electric charge. Usually, for example, in a wire, all of the electric charges have the same sign and move in the same direction.

The two charges we are considering have opposite signs. One charge is positive, and one charge is negative. So, can these two opposite-sign charges move to produce an electric current? Actually, yes. If opposite-sign charges move in opposite directions to each other, this produces an electric current. Electric current is positive in the direction of motion of positive charge. Negative charge moving in the opposite direction to a positive charge produces an electric current in the same direction as the current produced by the motion of the positive charge.

It is very important to remember however that the question states that the charges are fixed in place. They cannot move. If the charges cannot move, then there can be no motion of charge. And so there cannot be an electric current. Option (A) is therefore incorrect.

But what about option (B)? Can there be an electric potential difference between the charges? Electric potential difference is defined as the work needed to move a unit charge between two points. And work is done by a force to move an object in a particular direction. Let’s think about how these charges became separated. Initially, with no forces holding them in place, they must have been next to each other. If we want to separate these charges, we’ll have to apply forces to overcome the attractive forces pulling them together. When we apply these forces, we’re doing work on the charges to separate them. And so, by separating these charges, we have created an electric potential difference between them.

Therefore, answer option (B) is the correct answer. The separation of positive and negative charges creates an electric potential difference between them.

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