Question

A magnet is suspended in such a way that it oscillates in the horizontal plane. It makes 20 oscillations per minute at a place where dip angle is 30° and 15 oscillations per minute at a place where dip angle is 60°. Ratio of total earth’s magnetic field at the two places is

(a)  3√3 :8 

(b) 16 : 9√3

(c)  4 : 9

(d)  2√2 : 3

Answer 1

Correct option (b) 16 : 9√3

Explanation:

Let the total magnetic fields due to earth at two places be B₁ and B₂ . If the horizontal components be (B_H)1 and (B_H)₂ respectively then

(B_H)₁ = B₁ Cos 30° and (B_H)₂ = B₂ Cos 60°

Here T₁ = 3 sec. and T₂ = 4 sec.