JEE Main202118 Mar 2021Evening ShiftPhysicsMagnetic Effects of CurrentActual
A proton and an α -particle, having kinetic energies K p and K α , respectively, enter into a magnetic field at right angles. The ratio of the radii of the trajectory of proton to that of α -particle is 2 : 1 . The ratio of K p : K α is:
Options
- A1 : 8
- B8 : 1
- C1 : 4
- D4 : 1
Correct answer
D. 4 : 1
Step-by-step solution
r = m v q B = p q B    m α m p = 4 r p r α = p p q p q α p α = 2 1 p p p a = 2 q p q a = 2 1 2 p p p α = 1 K p K α = p p 2 p α p m α m p = 1 4