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In the above diagram, a strong bar magnet is moving towards solenoid-2 from solenoid-1. The direction of induced current in solenoid-1 and that in solenoid-2, respectively, are through the directions:
Solenoid 1 attracts receding N-pole (forms S-pole); Solenoid 2 repels approaching S-pole (forms S-pole)!
As the bar magnet moves to the right with velocity v, the North pole moves away from Solenoid 1, causing a decrease in magnetic flux through Solenoid 1 directed to the left. According to Lenz’s law, the induced current must oppose this decrease by creating an attractive force (i.e. generating a South pole on its right face facing the magnet).
A South pole on the right end means that when viewed from the right, the current circulates clockwise. Tracing the turns wound over the core, current enters through terminal A, passes over the top turns towards the right, and emerges through terminal B. Therefore, current flows from A to B.
The South pole of the bar magnet is moving closer to Solenoid 2. To oppose this approach, the left face of Solenoid 2 facing the magnet must develop a South magnetic pole to exert a repulsive force on the approaching South pole.
A South pole on the left end means that when viewed from the left, current circulates clockwise. Tracing the winding on Solenoid 2, the current enters from terminal D, goes up the back, over the top forward, and exits at terminal C. Hence, the current flows in the direction DC.
Diagnose every choice: Know exactly why the right option works and why distractors fail.
Incorrect current direction for Solenoid 2; current flows from D to C, not C to D.
Incorrect current direction for Solenoid 1.
Precisely adheres to Lenz’s law for both receding North and approaching South poles.
Completely inverts both solenoid current directions.
Students often determine whether induced polarity is North or South correctly, but get confused when determining clockwise vs anticlockwise because they view from the wrong side of the solenoid.
"The polarity of induced emf is always such that it tends to produce a current that opposes the change in magnetic flux that produces it."
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