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NTA Abhyas JEE Main2020PhysicsMagnetic Properties of MatterPractice

Two bar magnets A and B are placed one over the other and are allowed to Vibrate in a vibration magnetometer. They make 20 oscillations per minute when the similar poles of A and B are on the same side, while they make 15 oscillations per minute when their opposite poles lie on the same side. If M A and M B are the magnetic moments of A and B and if M A > M B , the ratio of M A and M B is

Options

  1. A4 : 3
  2. B25 : 7
  3. C7   :   5
  4. D25   :   16

Correct answer

B. 25 : 7

Step-by-step solution

Ratio of magnetic moments of two magnets of equal size when in same and different position is M A M B = T d 2 + T s 2 T d 2 - T s 2 = v ⁡ d 2 + v ⁡ s 2 v ⁡ d 2 - v ⁡ s 2 M A M B = 2 0 2 + 1 5 2 2 0 2 - 1 5 2 = 400 + 225 400 - 225 M A : M B = 25 : 7

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