Question

The ratio of speed of an electron in $I$ Bohr orbit of $H$-atom to speed of light in vacuum is:

• A. $7.29$
• B. $7.29\times {10}^{-3}$
• C. $72$
• D. ${10}^{-2}$

Answer 1

The correct option is B $7.29\times {10}^{-3}$

As we know, velocity of electron in I orbit of H is,
$u_e=2.188\times {10}^8$ $cm/sec$

and veocity of light in vacuum is
$u_l=3.0\times {10}^{10}$ $cm/sec$

So, their ratio is
$\frac{u_e}{u_l}=\frac{2.188\times {10}^8}{3.0\times {10}^{10}}=7.29\times {10}^{-3}$

Therefore, the correct option is (B)