A small bar magnet is moved through a coil at constant speed from one end to the other. Which of the following series of observations will be seen on the galvanometer G attached across the coil?
Three positions shown describe: (a) the magnet's entry (b) magnet is completely inside and (c) magnet's exit
(A)(see structure)✓ Correct
(B)(see structure)
(C)(see structure)
(D)(see structure)
Answer: (A)
Solution
By Faraday's law an emf appears only while the flux linked with the coil is changing. As the magnet enters, the flux grows and the galvanometer deflects one way, say to the right. While the magnet is wholly inside and moving at constant speed the flux through the coil is momentarily steady, so no emf is induced and the needle rests at zero. As the magnet leaves, the flux falls and, by Lenz's law, the induced current reverses, deflecting the needle the opposite way, to the left. The sequence is therefore a deflection one way, then no deflection, then a deflection the other way.
JEE Main · 2020 · 04 Sep 2020 · Shift 1 · Single correct option
