Question

Assertion :Consider two identical charges placed at a distance 2d apart, along the x-axis. The state of equilibrium of a positive test charge placed at the point O midway between them is stable for displacements along the x-axis. Reason: Force on test charge is zero.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Answer 1

The correct option is B Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion

On displacement along X-axis, the net force on the charge becomes non-zero and is always towards origin $O$.And hence the force on test charge moves the charge back to $O$ restoring its stabitlity.

But when, charge is displaced along Y-axis, net force on it becomes along Y-axis in direction of displacement and not along origin so as to restore its initial position.

Hence. the charge is stable for displacement along X-axis.

As both charges are equal and equidistant from $O$, net field at $O$ becomes zero.

Hence force on test charge becomes zero.

Hence, both Assertion and Reason are correct but Reason is not correct explanation of Assertion.

Answer-(B)