Science (086) — CBSE Class 10 board question

(i)

(1) If the current is increased, the force on the conductor increases, so the displacement towards the left will be greater.

(2) A stronger horse-shoe magnet produces a stronger magnetic field, so the force increases and the displacement towards the left will be greater.

(3) If the direction of current is reversed, the direction of force reverses, so the conductor will now be displaced towards the right.

(ii) Fleming's Left-Hand Rule — Stretch the thumb, forefinger, and middle finger of the left hand so that they are mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of current, then the thumb points in the direction of the force (motion) on the conductor.

Source: Chapter 12, Section 12.3

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• For part (i), the key idea is that force ∝ current × magnetic field strength; increasing either increases displacement. Reversing current reverses the direction of force (Fleming's left-hand rule).
• For part (ii), examiners expect the name of the rule and a complete statement covering all three — field, current, and force/motion. Missing even one finger's direction loses marks.
• Keep the rule statement precise: forefinger = field, middle finger = current, thumb = force/motion.