A magnetic compass needle oscillates 30 times per minute at a place where the dip is 45°, and 40 times per minute where the dip is 30. If B1 and B2 are respectively the total magnetic field due to the earth at the two places, then the ratio B1/ B2 is best given by :
(1) 1.8 (2) 2.2 (3) 0.7 (4) 3.6
