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JEE Main 2021 (25 Jul, Shift 2) · Moving Charge in a Magnetic Field

Moving Charge in a Magnetic Field question from JEE Main 2021 (25 Jul, Shift 2)

Q65JEE Main 2021 · 25 JUL · SHIFT 2Easy

Moving Charge in a Magnetic Field

Two ions having same mass have charges in the ratio 1: 2. They are projected normally in a uniform magnetic field with their speeds in the ratio 2: 3. The ratio of the radii of their circular trajectories is:

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Answer: (b)

  1. r=mvqB⇒r∝vqr = \dfrac{mv}{qB} \Rightarrow r \propto \dfrac{v}{q} for the same mm
  2. r1r2=v1v2⋅q2q1=23×21=43\dfrac{r_1}{r_2} = \dfrac{v_1}{v_2}\cdot\dfrac{q_2}{q_1} = \dfrac{2}{3}\times\dfrac{2}{1} = \dfrac{4}{3}
  3. So the answer is (b) 4:34:3.
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