An electric current passes through a long straight copper wire. At a distance of 5 cm from the straight wire, the magnetic field is B. What is the magnetic field at a distance of 20 cm from the wire ?

Options

A. `B/6`
B. `B/4`
C. `B/3`
D. `B/2`

Answer

B

Explanation

`B_(P)=(mu_(0))/(2pi)I/5=B,B_(Q)=(mu_(0))/(2pi)I/20=B/4`