A thin wire of length `l` is carrying a constant current. The wire is bent to form a circular coil. If radius of the coil, thus formed, is equal to R and number of turns in it is equal to `n`, then which of the following graphs represent (s) variation of magnetic field induction (B) at centre of the coil

Options

A.
B.
C.
D.

Answer

B, C

Explanation

`2pi Rn = l implies n = (1)/(2pi R)`
`B = (mu_(0))/(4pi) * (2pi "ni")/( R) = mu_(0) *(li)/(4pi R^(2)) implies B prop (1)/(R^(2)), R to 0 , B to oo`
and `R to oo, B to 0` [ option (b) `to` correct]
`R = (1)/(2pi n) , B = (mu_(0))/(pi) * (2pi "ni")/(R )`
`implies B prop n^(2) to` Parabola [option (c) `to` correct]