Question

The magnetic field along axis at a point at a distance d of a short, bar magnet will be

• A. $\frac{{\mu }_0}{3\pi }\times \frac{M}{d^3}$
• B. $\frac{{\mu }_0}{\pi }\times \frac{M}{d^3}$
• C. $\frac{{\mu }_0}{2\pi }\times \frac{M}{d^3}$
• D. $\frac{{\mu }_0}{4\pi }\times \frac{M}{d^3}$

Answer 1

Answer: (C)

The magnetic field with the effect of the bar magnet at an axial position at a distance is given by $B=\frac{{\mu }_0}{4\pi }\times \frac{2Md}{{(d^2-l^2)}^2}$ For a short bar magnet $l^2<<d^2$ Hence $B=\frac{{\mu }_0}{4\pi }\times \frac{2M}{d^3}=\frac{{\mu }_0}{2\pi }\times \frac{M}{d^3}$