Question

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:

• 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

Hint:

When analyzing assertions and reasons in physics, remember that the reason should adequately explain the assertion. If not, mark them as correct but not the correct explanation.

Answer 1

The Correct Option is D

Analysis of Assertion (A) and Reason (R) is as follows:

Assertion (A): This assertion posits that a polar linear isotropic dielectric possesses a net dipole moment even without an applied external electric field. This implies a spontaneous dipole alignment, contradicting the established behavior of polar dielectrics where external fields induce net moments.

Reason (R): This reason asserts that in the absence of an external electric field, the permanent dipoles within a polar dielectric exhibit random orientation. This random arrangement leads to the cancellation of individual dipole moments, resulting in a zero net dipole moment.

Based on this evaluation:

(A) is correct but (R) is not correct

Both (A) and (R) are correct but (R) is not the correct explanation of (A)

Both (A) and (R) are correct and (R) is the correct explanation of (A)

(A) is not correct but (R) is correct

The conclusion is that option (A) is not correct but (R) is correct is the most fitting. Assertion (A) is factually incorrect by suggesting a net dipole moment without an external field, whereas reason (R) accurately describes the random dipole orientation in such conditions.