Two concentric and coplanar coils have radii a and `b ( gt gt a)` as shows in Fig. Resistance of the inner coil is `R`. Current in the outer coil is increased from `0` to `i`, then the total charge circulating the inner coil is

Options

A. `(mu_(0) i a^(2)pi)/(2RB)`
B. `(mu_(0)i ab)/(2R)`
C. `(mu_(0)i a b)/(2a)(pi b^(2))/(R )`
D. `(mu_(0)ib)/(2pi R)`

Answer

A

Explanation

`Delta q = (Delta phi)/(R ), phi = 0, phi_(f) = ((mu_(0))/(2)(i)/(b))(pi a^(2)) = (mu_(0)i a^(2) pi)/(2b)`
`:. Delta phi = phi_(f) - phi_(i) = (mu_(0) i a^(2) pi)/(2b), " "` So, `Delta q = (mu_(0) i a^(2)pi)/(2 Rb)`