Consider a long, straight wire of cross-sectional area A carrying a current i. Let there be n free electrons per unit volume. An observed places himself on a trolley moving in the direction opposite to the current with a moving in the direction opposite to the current with a speed `(v= i/nAe) and separated from the wire by a distance r. The magnetic field seen by the observer is very nearly

Options

A. `(mu_(0)i)/(2pi r)`
B. zero
C. `(mu_(0)i)/(pi r)`
D. `((2 mu_0)i)/(pi r)`

Answer

A