Q.

N equally spaced charges each of value q, are placed on a circle of radius R. The circle rotates about its axis with an angular velocity ω as shown in the figure. A bigger Amperian loop B encloses the whole circle where as a smaller Amperian loop A encloses a small segment. The difference between enclosed currents, IAIB, for the given Amperian loops is          [2025]

1 N22πqω  
2 2πNqω  
3 N2πqω  
4 Nπqω  

Ans.

(3)

I=Nq2πω=Nqω2π

Now for bigger Amperian loop (loop B)

IB(enclosed)=0

And for smaller Amperian loop (loop A)

|IA(enclosed)|=I=Nqω2π

So, |IAIB|=Nqω2π