A and B are two concentric circular conductors of centre O and carrying currents i1  and i2 as shown in the adjacent figure. If ratio of their radii is 1 : 2 and ratio of the flux densities at O due to A and B is 1 : 3, then the value of i1/i2 is

 

(a)  16                       (b)  14                                

 (c)  13                       (d)  12                                                                                                          

(a) r1 : r2  and  B1:B2=1:3   We know that 

    B=μ04π·2πnir i1i2=B1r1B2r2=1×13×2=16

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