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 :
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 :
- (A)(A) is correct but (R) is not correct
- (B)Both (A) and (R) are correct but (R) is not the correct explanation of (A)
- (C)Both (A) and (R) are correct and (R) is the correct explanation of (A)
- (D)(A) is not correct but (R) is correct✓ Correct
Answer: (D)
Solution
For a polar dielectric in the absence of an external electric field, the permanent dipoles are randomly oriented in all directions. Due to this random orientation, the vector sum of all dipole moments averages to zero, so the net dipole moment . Therefore, Assertion (A) is incorrect. Reason (R) is correct: polar dielectrics do have permanent dipoles that remain randomly oriented when no external field is applied. Hence (A) is not correct but (R) is correct.
JEE Main · 2025 · 02 Apr 2025 · Shift 2 · Single correct option