Question

What is the magnitude of axial field due to a bar magnet of length 3 cm at a distance of 75 cm from its mid-point if its magnetic moment is $0.6\, A\, m^2$?

• A. $0.013\, ?T$
• B. $0.113\, ?T$
• C. $0.284\, ?T$
• D. $0.313\, ?T$

Answer 1

Answer: (C)

$0.284\, ?T$

Answer 2

Here $m=0.6\,A\,m^{2}, r=75\,cm=0.75\,m$ $B_{axial}=\frac{\mu_{0}}{4\pi}.\left(\frac{2m}{r^{3}}\right)=10^{-7}\times\frac{2\times0.6}{\left(0.75\right)^{3}}$ $\therefore B_{axial}=2.84\times10^{-7}\,T=0.284\,\mu T.$