Two plane circular coilds P and Q have radii `r_(1)` and `r_(2)`, respectively, `(r_(1) lt lt r_(2))` and are coaxial as shown in fig. The number of turns in P and Q are respectively `N_(1)` and `N_(2)`. If current in coil Q is varied steadily at a rate x ampere/second then the induced emf in the coil P will be approximatery -

Options

A. `mu_(0)N_(1)N_(2)pir_(1)^(2)`
B. `mu_(0)N_(1)N_(2)pi r_(1)^(2)x`
C. `mu_(0)N_(1)N_(2)pi r_(1)^(2) x//2r_(2)`
D. zero

Answer

C

Explanation

`phi = Mi`
`e = (Mdi)/(dt) = Mx = (mu_(0)N_(1)N_(2)pir_(1)^(2)x)/(2r_(2))`