Q 1 :

A compass needle oscillates 20 times per minute at a place where the dip is 30° and 30 times per minute where the dip is 60°. The ratio of total magnetic field due to the earth at the two places respectively is 4x. The value of x is ___________ .          [2023]



(243)

Period of oscillation ∝1BH

T∝1Bcosθ ⇒ T1T2=B2cosθ2B1cosθ1

⇒ 60/2060/30=B2cos60°B1cos30° ⇒ 32=B23B1

⇒ 94=B23B1 ⇒ B1B2=493=4243