Question

$A$ $200$ turn closely wound circular coil of radius $15\, cm$ carries a current of $4 \,A$. The magnetic moment of this coil is

• A. $36.5 \, A\, m^{2}$
• B. $56.5 \, A\, m^{2}$
• C. $66.5 \, A\, m^{2}$
• D. $108 \, A\, m^{2}$

Answer 1

Answer: (B)

The magnetic moment is given by
$\left|\vec{m}\right|=NIA = NI \pi r^{2} =200\times4\times3.14\times\left(15\times10^{-2}\right)^{2}$
$=200\times4\times3.14\times15\times15\times10^{-4}$
$=56.5\,A\,m^{2}$