With a standard rectangular bar magnet the time period of a vibration magnetometer is 4 s. The bar magnet is cut parallel to its length into four equal pieces. The time period of vibration magnetometer when one piece is used (in second) (bar magnet breadth is small) is

Options

A. 16
B. 8
C. 4
D. 2

Answer

C

Explanation

Time period of bar magnet is given by,
`T=2pisqrt((I)/(MB)`
When a bar magnet is cut into '4' equal parts.
magnetic moment,
`M^(1)=M/4`
New moment of inertia,
`I^(1)=I/4`
therefore New time period,
`T=2pisqrt((I^(1))/(M^(1)B`
There is no change in time period
Hence, `T=T^(1)=4sec.`