Question

A magnetic needle has a magnetic moment $5.0\times {10}^{-2}A{m}^2$ and moment of inertia $8.5\times {10}^{-7}Kg{m}^2$. It performs oscillation of time period $0.65$s. What is the magnitude of the magnetic field?

• A. $0.0016$T
• B. $0.16$T
• C. $1.6$T
• D. $16$T

Answer 1

The correct option is A $0.0016$T

Here, $m=5.0\times {10}^{-2}A{m}^2$
$T=0.65s,I=8.5\times {10}^{-7}Kg{m}^2$

The magnetic field
$B=\frac{4{\pi }^{2}I}{m{T}^2}=\frac{4\times (3.14{)}^2\times 8.5\times {10}^{-7}}{5\times {10}^{-2}\times (0.65{)}^2}=158.69\times {10}^{-5}T=0.0016T$