Why does the electric field inside a dielectric decrease when it is placed inan external electric field?

When a dielectric material is placed in an external electric field, the electric field induces a polarization in the dielectric. This means that the positive and negative charges within the dielectric material are displaced in opposite directions, creating an induced electric field.

Here are the steps explaining why the electric field inside a dielectric decreases when it is placed in an external electric field:

1. Polarization: When a dielectric is placed in an external electric field, the positive and negative charges within the dielectric material get displaced in opposite directions. This displacement of charges creates an induced electric field inside the dielectric.

2. Induced Electric Field: The induced electric field inside the dielectric is in the direction opposite to that of the external electric field. This is due to the alignment of the dipole moments (created due to the displacement of charges) in the direction opposite to the external electric field.

3. Decrease in Net Electric Field: The induced electric field inside the dielectric opposes the external electric field. As a result, the net electric field inside the dielectric is less than the external electric field. This is why the electric field inside a dielectric decreases when it is placed in an external electric field.

4. The decrease in the electric field results in a decrease in the voltage across the dielectric, which in turn decreases the stored energy. This is the reason why dielectrics are used in capacitors to increase their capacitance. The decrease in electric field allows the capacitor to store more charge for a given voltage, thereby increasing its capacitance.