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Question: A magnetic needle has magnetic moment 5.8 x 10-2 A m2 and moment of inertia of 7.8 x 10-6 kg m2, it ...

A magnetic needle has magnetic moment 5.8 x 10-2 A m2 and moment of inertia of 7.8 x 10-6 kg m2, it performs 12 complete oscillations in 6.0 s. What is the magnitude of magnetic field?

A

0.011 T

B

0.021 T

C

0.031 T

D

0.041 T

Answer

0.021 T

Explanation

Solution

: Here, time period of oscillations

T=6.012=0.5 s\mathrm { T } = \frac { 6.0 } { 12 } = 0.5 \mathrm {~s}

Now, magnetic field, B=4π2ImT2\mathrm { B } = \frac { 4 \pi ^ { 2 } \mathrm { I } } { \mathrm { mT } ^ { 2 } }

Here,m2,π=3.14\mathrm { m } ^ { 2 } , \pi = 3.14

m=5.8×10−2Am2\mathrm { m } = 5.8 \times 10 ^ { - 2 } \mathrm { Am } ^ { 2 }