A compass needle of oscillation magnetometer oscillates 20 times per minute at a place P of dip 30°. The number of oscillations per minute become 10 at another place Q of 60° dip. The ratio of the total magnetic field at the two places (BQ : BP) is
1
√3 : 4
2
4 : √3
3
√3 : 2
4
2 : √3
5
Question Not Attempted