Q.

Suppose a long solenoid of 100 cm length, radius 2 cm having 500 turns per unit length, carries a I=10sin(ωt) A,  where ω=1000 rad/s. A circular conducting loop (B) of radius 1 cm coaxially slides through the solenoid at speed v = 1 cm/s. The r.m.s. current through the loop when the coil B is inserted 10 cm inside the solenoid is α2 μA. The value of α is ______.

[Resistance of the loop =10Ω]    [2026]

1 280  
2 80  
3 197  
4 100  

Ans.

(3)

EMF induced ε=AdBdt=Aμ0ndidt

ε=Aμ0ni0ωcosωt

current induced i=εR=πr2μ0ni0ωRcosωt

So i=πr2μ0ni0ω2R

=π×10-4×4π×10-7×500×10×1032×10

=20π22×10-6

=1972μA