A long circular tube of length `10 m` and radius ` 0.3 m` carries a current `I` along its curved surface as shown . A wire - loop of resistance `0.005 ohm` and of radius `0.1 m` is placed inside the tube its axis coinciding with the axis of the tube . The current varies as `I = I_(0)cos(300 t)` where `I_(0)` is constant. If the magnetic moment of the loop is `Nmu_(0)I_(0) sin (300 t)`, then 'N' is

Explanation

Flux through circular ring `phi=(mu_(0)ni)pir^(2) rArrphi=(mu_(0))/Lpir^(2)I_(0)cos300t rArr i=(dphi)/(Rdt)`
`i=(mu_(0)pir^(2)I_(0))/(RL).sin 300 txx300=mu_(0)I_(0)sin 300t[(pir^(2).300)/(RL)] rArr M=I.pir^(2)`
`=mu_(0)I_(0)sin 300t[(pi^(2)r^(4).300)/(RL)] `(Take `pi^(2)=10`)=`(10xx10^(-4)xx300)/(100xx10) rArr N=6`