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JEE MAIN - Physics (2025 - 2nd April Evening Shift - No. 3)

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 :

Both (A) and (R) are correct and (R) is the correct explanation of (A) 2.
Both (A) and (R) are correct but (R) is not the correct explanation of (A)
(A) is not correct but (R) is correct
(A) is correct but (R) is not correct

Explanation

Assertion (A): The net dipole moment of a polar linear isotropic dielectric substance is not zero, even when there is no external electric field.

Reason (R): In the absence of an external electric field, the different permanent dipoles in a polar dielectric substance are oriented in random directions.

Explanation:

Assertion (A): The statement is incorrect. In a polar linear isotropic dielectric substance, the net dipole moment is zero when an external electric field is absent. This is because the dipoles within the material are randomly oriented and cancel each other out.

Reason (R): The statement is correct. In the absence of an external electric field, the dipoles in a polar dielectric substance remain inherently polarized but are oriented randomly. This randomness in orientation leads to a cancellation of the net dipole moment.

Therefore, while the reason is correct, it does not support the validity of the assertion as stated.

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