A student was asked to perform an experiment to study the force on a current carrying conductor in a magnetic field. He took a small aluminum rod AB, a strong horse shoe magnet, some connecting wires, a battery and a switch and connected them as shown. He observed that on passing current, the rod gets displaced. On reversing the direction of current, the direction of displacement also gets reversed.
On the basis of your understanding of this phenomenon, answer the following questions:
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Model Answer
(a) When current flows through conductor AB, it experiences a mechanical force due to the interaction between the current-carrying conductor and the magnetic field of the horseshoe magnet. This force causes the rod to get displaced.
(b) Fleming's Left-Hand Rule — Stretch the thumb, forefinger, and middle finger of the left hand 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 force on the conductor.
(c)
(i) Using Fleming's Left-Hand Rule: magnetic field points from N to S (vertically, say downward), current flows from B (North) to A (South), i.e., southward. The rod will be displaced towards East.
(ii) Electric motor and Loudspeaker (moving-coil)
Source: Chapter 13 – Magnetic Effects of Electric Current, NCERT Class 10 Science
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Explanation
- (a) The key concept is force on a current-carrying conductor in a magnetic field — always state both factors (current + magnetic field = force).
- (b) Examiners expect the full statement of Fleming's Left-Hand Rule, not just the name. Name + rule = full marks.
- (c)(i) Apply the rule carefully: N pole is at bottom → field goes upward (N→S inside magnet = bottom to top); current B→A = North to South. Using FLHR: field ↑, current direction South → force acts East (or West depending on exact orientation — apply rule consistently). Examiners look for correct application of the rule.
- (c)(ii) Any two valid devices are acceptable: electric motor, electric bell, loudspeaker, galvanometer.