Question

A current of $1A$ is passed through a straight wire of length 2.0 m. The magnetic field at a point in air at a distance of 0.3 m from either end of the wire and lying on the axis of wire will-be

• A. $\frac{{\mu }_o}{2\pi }$
• B. $\frac{{\mu }_o}{4\pi }$
• C. $\frac{{\mu }_o}{8\pi }$
• D. zero

Answer 1

Answer: (D)

zero

Since $B=\frac{{\mu }_{o}i\overrightarrow{L}\times \overrightarrow{d}}{4\pi d^2}$

since point lies on the current flowing axis ,so $\overrightarrow{L}\times \overrightarrow{d}=0$

So $B=0$