Science — CBSE Class 10 board question

(b) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A). Field lines don't intersect because that would imply two directions of field at one point, which is impossible. Reason (R) merely defines field lines.

• A is true: Two magnetic field lines never intersect. The correct reason is that if they did, there would be two tangents at the point of intersection, meaning two directions of the magnetic field at the same point — which is impossible.
• R is true: Field lines are indeed imaginary lines; the tangent at any point gives the field direction. But this statement only defines field lines; it does not explain why they cannot intersect.
• So both statements are correct, but R does not explain A → option (b).