Question

If the speed of electron in Bohr first orbit of hydrogen atom be $x$, then speed of the electron in 3rd orbit is:

• A. $\frac{x}{9}$
• B. $\frac{x}{3}$
• C. 3x
• D. 9x

Answer 1

The correct option is B $\frac{x}{3}$

Velocity of electron in the $n^{th}$ orbit of hydrogen atom,
$v=\frac{2.188\times {10}^8}{n}{\text{cm s}}^{-1}$
Given, velocity in first orbit,
$v_1=\frac{2.188\times {10}^8}{1}{\text{cm s}}^{-1}=x$
Velocity in third orbit
$v_3=\frac{2.188\times {10}^8}{3}cm{s}^{-1}=\frac{x}{3}$