A circular current carrying coil has a radius R. The distance from the centre of the coil on the axis where the magnetic induction will be 18th to its value at the centre of the coil, is

(a) R3                       (b)  R3

(c) 23R                     (d) 23R

(b)

BcentreBaxis=1+x2R23/2, also Baxis=18Bcentre81=1+x2R23/22=1+x2R21/24=1+x2R23=x2R2x2=3R2x=3R

 

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