Q72 / 90 · JEE Main 2022 (27 Jul Shift 2) · Physics

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:

  • Correct answer
    A
    3:4
  • B
    4:3
  • C
    3:2
  • D
    2:3

Solution

At point P the needle oscillates 20 times per minute. Therefore, time period TP=6020= 3 s and at point Q, TQ=6010=6 s.

The time period of oscillation magnetometer is given by,

T=2πIBHM

⇒TP=3=2πIBPcos30°M

And TQ=6 s=2πIBQcos60°M

Taking ratio,

36=1 BP32×BQ2

⇒34=BQBP

⇒BQ:BP=3:4

Hence, the correct answer is option: 'A'.

Relevant Questions