A magnetic needle has magnetic moment 5.8 x 10 A m and moment of inertia of 7.8 x 10 kg m', it performs 12 complete oscillations in 6.0 s. What is the magnitude of magnetic field?

Options

A. 0.011 T
B. 0.021 T
C. 0.031 T
D. 0.041 T

Answer

B

Explanation

Here, time period of oscillations
`T=(6.0)/(12)=0.5 s`
Now, magnetic field, `B=(4pi^(2)I)/(mT^(2))`
Here, `" "I= 7.8xx10^(-6)"kg m"^(2), pi=3.14`
`" "m=5.8xx10^(-2)"A m"^(2)`
`therefore" "B=(4xx(3.14)^(2)xx7.8xx10^(-6))/(5.8xx10^(-2)xx(0.5)^(2))=0.021` T