The ratio of the speed of the electron in the first Bohr orbit of hydrogen and the speed of light is equal to (where e, h and c have their usual meanings)
Answer & explanation
Correct answer: option 4
Speed of electron in nth orbit (in CGS) $v_n=\frac{2 \pi Z e^2}{n h}(k=1)$
For first orbit H2 ; n = 1 and Z = 1
So $v=\frac{2 \pi e^2}{h} \Rightarrow \frac{v}{c}=\frac{2 \pi e^2}{h c}$