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Wave Optics

Question
CBSEENPH12039826

A proton carrying 1 MeV kinetic energy is moving in a circular path of radius R in the uniform magnetic field. What should be the energy of an alpha particle to describe a circle of the same radius in the same field.

  • 2 MeV

  • 1 MeV

  • 0.5 MeV

  • 4 MeV

Solution

B.

1 MeV

For space proton
straight r space equals space fraction numerator square root of 2 straight m left parenthesis KE right parenthesis end root over denominator qB end fraction
So
straight q space proportional to space square root of straight m left parenthesis KE right parenthesis end root

Hence space fraction numerator straight e over denominator 2 straight e end fraction space equals space square root of fraction numerator left parenthesis straight m subscript straight p right parenthesis left parenthesis 1 space Mev right parenthesis over denominator left parenthesis 4 straight m subscript straight p right parenthesis left parenthesis KE right parenthesis end fraction end root
1 fourth space equals fraction numerator 1 space MeV over denominator 4 KE end fraction

KE space equals 1 space MeV