A mono energetic electron beam with electron speed of $5.20 \times 10^6 ms^{-1}$ is subjected to a mognetic field of $1.30 \times 10^{-4}\;T$ , normal to the beam velocity .What is the radius of the circle traced by the beam , given $\large\frac{e}{m}$ for electron equals $1.76 \times 10^{11} ckg^{-1}$Is the formula you employ valid for calculating radius of the path of 20 Mev electron beam ? If not in what way is it modified ?

Question

$\begin{array}{1 1} R= \large\frac{m_o v}{eB \sqrt{1-\Large\frac{v^2}{c^2}}} \\ R= \large\frac{m_o e}{vB \sqrt{1-\Large\frac{v^2}{c^2}}} \\ R= \large\frac{m_o v}{eB \sqrt{1-\Large\frac{c^2}{v^2}}} \\ R= \large\frac{m_o^2}{vB \sqrt{1-\Large\frac{c^2}{v^2}}}\end{array} $