Which one of the following statements is true concerning the strength of the electric field between two oppositely charged parallel plates ?

Options

A. It is zero midway between the plates
B. It is a maximum midway between the plates
C. It is maximum near the positively charged plate
D. It is constant between the plate except near the edges.

Answer

To determine which statement is true concerning the strength of the electric field between two oppositely charged parallel plates, we can analyze the properties of the electric field in that region.

### Step-by-Step Solution:

1. **Understanding Electric Field Between Plates**:
- When two parallel plates are oppositely charged, an electric field is established between them. The positive plate creates an electric field directed away from it, while the negative plate creates an electric field directed towards it.

2. **Characteristics of the Electric Field**:
- The electric field (E) between two infinite parallel plates is uniform and constant in magnitude. This means that the strength of the electric field does not change with position between the plates.

3. **Electric Field at Different Points**:
- Inside the plates (between them), the electric field is constant.
- Near the edges of the plates (fringe effects), the electric field may vary and is not uniform. However, this variation is negligible when considering the central region between the plates.

4. **Evaluating the Given Statements**:
- **Option 1**: "0 midway" - This is incorrect because the electric field is not zero; it has a constant value.
- **Option 2**: "Maximum midway between the plates" - This is also incorrect; the electric field is constant, not maximum at the midpoint.
- **Option 3**: "Constant between the plates except near the edges" - This statement is true as the electric field is indeed constant in the central region but may vary near the edges.

5. **Conclusion**:
- The correct statement regarding the electric field strength between two oppositely charged parallel plates is that it is constant between the plates, except near the edges.

### Final Answer:
The true statement is: "It is constant between the plates except near the edges."