The strength of the magnetic field at a point `r` near a long straight current carrying wire is `B`. The field at a distance `r/2` will be

Options

A. `(B)/(2)`
B. `(B)/(4)`
C. 2B
D. 4B

Answer

C

Explanation

Magnetic field distanc r near a stright curretn carrying wire is given by
`B=(mu_(0))/(4pi)*(2l)/(r) rAr B prop (1)/(r)`
`:. (B_(1))/(B_(2))=(r_(2))/(r_(1)) or (B)/(B_(2))=(r//2)/(r)`
`:. B_(2)=2B`