An infinitely long wire carrying current I is along Y-axis such taht its one end is at point A(0,b) while the wire extends upto `+oo`. The magnitude of magnetic field strength at point (a,0) is

Options

A. `(mu_0I)/(4pia)(1+b/(sqrt(a^2+b^2)))`
B. `(mu_0I)/(4pia)(1-b/(sqrt(a^2+b^2)))`
C. `(mu_0I)/(4pia)(b/(sqrt(a^2+b^2)))`
D. none of these

Answer

B

Explanation

(b) `B=(mu_0I)/(4pi) i/a [sin90+(sin(- theta))]=(mu_0)/(4pi) i/a(1-sin theta)`
`=(mu_0)/(4pi) i/a(1-b/(sqrt(a^2+b^2)))`