Question

I have an electric field E across a region in vacuum. I now place a dielectric here. If I’m able to measure the electric field inside the dielectric, I will notice that it has

• A. Increased
• B. Decreased
• C. Stayed the same
• D. Vanished

Answer 1

The correct option is B Decreased

When a field is applied across a dielectric, it polarizes the dielectric medium. That is, if it were a polar dielectric, all the dipole moments of the molecules will align along the field. If it were a non-polar dielectric, there would be charge separation in the molecules caused by the field. The centre of the negative charge of the molecule will move away from the centre of positive charge of the molecule and the molecules now get an induced dipole moment. These dipoles now rotate and align themselves along the electric field.

Now, the dipole has unbalanced negative charges on one side and unbalanced positive charges on another side. This causes an induced field inside the dielectric due to these “sheets” of charge on opposite faces of the dielectric. This induced field $\overrightarrow{E_p}$ will be opposite to the applied electric field. Thus the net field inside the dielectric will be reduced to $|\overrightarrow{E_0}-\overrightarrow{E_p}|$