Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
**Assertion (A):** Net dipole moment of a polar linear isotropic dielectric substance is not zero even in the absence of an external electric field.
**Reason (R):** In absence of an external electric field, the different permanent dipoles of a polar dielectric substance are oriented in random directions.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer: (D) (A) is not correct but (R) is correct
Each molecule of a polar dielectric has a permanent dipole moment, but without an external field thermal agitation keeps these dipoles randomly oriented. Their vector sum is zero, so the net dipole moment of the substance is zero.
So (R) is correct and (A) is wrong.
Solution by Sreeraj P, M.Sc Physics