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

In considering the given Assertion (A) and Reason (R), we start by analyzing each statement:

Assertion (A): The statement mentions that the net dipole moment of a polar linear isotropic dielectric is nonzero even without an external electric field. This assertion implies that there is a preferential alignment of the dipoles resulting in a non-zero net dipole moment in the absence of an external force, which is contrary to the basic understanding of polar dielectrics.

Reason (R): It states that without an external electric field, the permanent dipoles in a polar dielectric are oriented randomly. This aligns with our understanding that in such a case, the random order of dipoles cancels out each other's effects, leading to a net dipole moment of zero.

Hence, upon 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

We conclude that option (A) is not correct but (R) is correct is the most appropriate. The assertion (A) incorrectly suggests a net dipole without an external field, while the reason (R) accurately describes the dipole behavior.