Physics

Problem

Which one of the following expressions gives the magnitude of the magnetic field at a distance

r

from an infinitely long straight conductor carrying a steady current

I

in air (symbols have their usual meaning)? a)

B=\dfrac{\mu_0 I}{\pi r}

B=\dfrac{\mu_0 I}{4\pi r}

B=\dfrac{\mu_0 I}{2\pi r}

B=\dfrac{\mu_0 I}{2 r}