In a vibration magnetometer, the time period of a bar magnet oscillating in horizontal componnt of earth's magnetic field is `2 sec`. When a magnet is brought near and parallel to it, the time period reduces to `1 sec`. The ratio `H//F` of the horizontal component `H` and the field `F` due to magnet will be

Options

A. `3`
B. `1//3`
C. `sqrt(3)`
D. `1//sqrt(3)`

Answer

B

Explanation

`T prop 1/sqrt(H) impliesT_(1)/T_(2)=sqrt(H_(2)/H_(1))implies2/1=sqrt((H+F)/H)impliesF=3H`
or `H/F=1/3`