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Question:

Two metallic rings A and B, identical in shape and size but having different resistivities ρA and ρB, are kept on top of two identical solenoids as shown in the figure. When current I is switched on in both the solenoids in identical manner, the rings A and B jump to heights hA and hB, respectively, with hA > hB. The possible relation(s) between their resistivities and their masses mA and mB is(are)

ρA < ρB and mA < mB

ρA < ρB and mA = mB

ρA > ρB and mA = mB

ρA > ρB and mA > mB

Solution:

As -dΦ/dt = emf is same, the current induced in the ring will depend upon resistance of the ring. Larger the resistivity smaller the current.