Question

The value of Planck's constant is $6.63\times {10}^{-34}Js.$ The velocity of light is $3\times {10}^{8}m/s.$ If the wavenumber of a quantum of light is $2.5\times {10}^7{m}^{-1}$, calculate its frequency.

• A. $7.5\times {10}^{15}{s}^{-1}$
• B. $3\times {10}^{15}{s}^{-1}$
• C. $11\times {10}^{15}{s}^{-1}$
• D. $5\times {10}^{15}{s}^{-1}$

Answer 1

The correct option is A $7.5\times {10}^{15}{s}^{-1}$

We know that, for electromagnetic radiation,

$c=\nu \lambda$
where, c is the velocity of light

$\Rightarrow \nu =\frac{c}{\lambda }$

$\Rightarrow =c\overline{\nu }$
(where, $\overline{\nu }$ is the wave number, which is the inverse of wavelength)

$=3\times {10}^8\times 2.5\times {10}^7{s}^{-1}$
$=7.5\times {10}^{15}{s}^{-1}$