A negative charge is placed between a pair of oppositely charged plates, as shown.

Question

Two horizontal parallel plates have a negatively charged sphere labeled X right in between them. The top plate is positive and the bottom plate is negative.

Which best describes the result of moving the charge to the point marked X?

Its electric potential energy increases because it has the same electric field.
Its electric potential energy increases because the electric field increases.
Its electric potential energy stays the same because the electric field increases.
Its electric potential energy stays the same because it has the same electric potential.

Answer 1

To determine the effect of moving the negative charge (sphere X) between the oppositely charged plates, we need to analyze the electric potential and electric field in the system.

1. Electric Field: Between two parallel plates, the electric field (\(E\)) is uniform and points from the positively charged plate to the negatively charged plate. In this case, since the charge at position X is negative, it will experience a force in the direction of the electric field (downwards towards the positively charged plate).

2. Electric Potential: The electric potential (\(V\)) is also uniform between the plates but varies with position. As we move in the direction of the electric field (down towards the positive plate), the potential decreases (since the negative charge moves to a lower potential).

3. Electric Potential Energy: The electric potential energy (\(U\)) of the charge is given by the relation \(U = qV\) where \(q\) is the charge and \(V\) is the electric potential. For a negative charge, if it moves to a point of lower electric potential, its electric potential energy decreases.

Given these points, when moving the negatively charged sphere X between the plates:

• The electric field itself does not change as long as we're between the plates.
• The electric potential decreases as it moves towards the positive plate.
• Therefore, the electric potential energy of the negative charge decreases, not stays the same or increases.

Considering the options provided:

1. "Its electric potential energy increases because it has the same electric field." (Incorrect)
2. "Its electric potential energy increases because the electric field increases." (Incorrect)
3. "Its electric potential energy stays the same because the electric field increases." (Incorrect)
4. "Its electric potential energy stays the same because it has the same electric potential." (Incorrect)

None of the options correctly describe the situation. The potential energy actually decreases as the negative charge moves towards the positive plate because it is moving to a lower electric potential.

However, if we have to select the best option based on potentially misleading language, the fourth option can imply constant electric potential in a certain area, which can be misleading but does not correctly reflect the change in potential energy. There may be a misunderstanding with the options provided, so clarification of their accurate nature would be required.