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JEE Main 2021 (18 Mar, Shift 2) · Moving Charge in a Magnetic Field

Moving Charge in a Magnetic Field question from JEE Main 2021 (18 Mar, Shift 2)

Q70JEE Main 2021 · 18 MAR · SHIFT 2Medium

Moving Charge in a Magnetic Field

A proton and an α\alpha-particle, having kinetic energies Kp and Kα\alpha respectively, enter into a magnetic field at right angles.

The ratio of the radii of trajectory of proton to that of α\alpha-particle is 2: 1. The ratio of Kp: Kα\alpha is:

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Answer: (b)

  1. K=q2B2r22m⇒K∝q2r2mK = \dfrac{q^2B^2r^2}{2m} \Rightarrow K \propto \dfrac{q^2r^2}{m}
  2. KpKα=(1)2(2)2/1(2)2(1)2/4=41\dfrac{K_p}{K_\alpha} = \dfrac{(1)^2(2)^2/1}{(2)^2(1)^2/4} = \dfrac{4}{1}
  3. So the answer is (b) 4 : 1.
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