Introduction:
A parallel plate capacitor consists of two parallel conducting plates separated by a distance. When a potential difference is applied across the plates, an electric field is established between them. However, this electric field may change under certain conditions.

Reasons for changing electric field:
There are several factors that can cause the electric field between the parallel plate capacitor to change:

1. Change in the applied potential difference:
When the potential difference applied across the plates changes, the electric field between them also changes. This is because the electric field is directly proportional to the potential difference. As the potential difference increases, the electric field strength also increases, and vice versa.

2. Change in the plate separation:
The electric field between the plates is inversely proportional to the distance between them. If the separation between the plates is increased, the electric field strength decreases, and if the separation is decreased, the electric field strength increases. Therefore, any change in the plate separation will result in a change in the electric field.

3. Change in the charge on the plates:
The electric field between the plates is also affected by the charge on the plates. If the charge on the plates increases, the electric field strength increases, and if the charge decreases, the electric field strength decreases. This is because the electric field is directly proportional to the charge.

4. Insertion of a dielectric material:
When a dielectric material is inserted between the plates of a parallel plate capacitor, it affects the electric field. The presence of a dielectric material increases the capacitance of the capacitor, which in turn decreases the electric field strength. This is because the dielectric material reduces the electric field by polarizing its molecules in the presence of the electric field.

Conclusion:
The electric field between the parallel plate capacitor can change due to various reasons such as changes in the applied potential difference, plate separation, charge on the plates, and the presence of a dielectric material. It is important to consider these factors when analyzing the behavior of a parallel plate capacitor and its electric field.