A proton and an electron moving with same kinetic energy enter uniform magnetic field at right- angle to its direction. The ratio of radii of their trajectories will be:

43 :1

The correct answer is Option 1: 43 : 1

$r=\frac{\sqrt{2m \, K.E}}{qB}$, q is same for both electron and proton.

$⇒r ∝ \sqrt{m}⇒\frac{r_p}{m_e}=\sqrt{\frac{m_p}{m_e}}=\sqrt{\frac{1.67\times 10^{-27}}{9.1\times 10^{-31}}}$

$⇒\frac{r_p}{r_e}=\sqrt{\frac{m_p}{m_e}}$

Since, mₚ ≈ 1836 mₑ

rₚ / rₑ = √1836 / 1 ≈ 43 :1

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