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Two point charges + Q and - Q having masses M and 2 M respectively, are projected from the same point with the same velocity v in the region of a uniform magnetic field B such that the velocity makes an angle θ with the magnetic field. If we neglect the mutual interaction between the particles, the distance from the point of projection where they will meet again for the first time is

Options

  1. A2 π Mv cos θ Q B
  2. B8 π Mv cos θ Q B
  3. Cπ Mv cos θ Q B
  4. D4 π Mv cos θ Q B

Correct answer

D. 4 π Mv cos θ Q B

Step-by-step solution

Here path will be helical T 1 = 2 π M QB T 2 = 2 π 2 M QB T 2 = 4 π M QB They will meet again when the first particle completes two revolutions and the second particle completes one revolution so distance will be given as d = v cos θ t = v cos θ . 2 2 π M QB = 4 π Mv cos θ QB

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