A proton carrying 1 MeV kinetic energy is moving in a circular path of radius R in uniform magnetic field. What should be the energy of an α -particle to describe a circle of same radius in the same field? (a) 2 MeV (b) 1 MeV (c) 0.5 MeV (d) 4 MeV

Answer: (b). Same r and B: K ∝ q²/m. (Kα)/(Kp) = ((2e)²/4m)/(e²/m) = 1 Kα = 1 MeV So the answer is (b) 1 MeV.

A proton carrying 1 MeV kinetic energy is moving in a circular path… | NEET 2012 (AIPMT, Mains)

Q104NEET 2012 · AIPMT · MAINSMedium

Moving Charge in a Magnetic Field

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

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Answer: (b)

Same $r$ and $B$ : $K \propto \dfrac{q^2}{m}$ .
$\dfrac{K_\alpha}{K_p} = \dfrac{(2e)^2/4m}{e^2/m} = 1$
$K_\alpha = 1$ MeV
So the answer is (b) 1 MeV.

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