Question

Find energy of each of the photons which
(i) correspond to light of frequency 3× ${10}^{15}$ Hz.

(ii) have wavelength of 0.50 Å.

Answer 1

( i ) Energy (E) of a photon is given by the expression,
E = hv
Where, h = Planck’s constant = 6.626 × ${10}^{–34}$ Js
ν = frequency of light = 3 × ${10}^{15}$ Hz
Substituting the values in the given expression of E:
E = (6.626 × ${10}^{–34}$ ) (3 × ${10}^{15}$) E = 1.988 × ${10}^{–18}$ J

(ii) Energy (E) of a photon having wavelength (λ) is given by the expression,
$E=\frac{hc}{\lambda }$
h = Planck’s constant = 6.626 × ${10}^{–34}$ Js
c = velocity of light in vacuum = 3 × ${10}^8$ m/s
Substituting the values in the given expression of E:
$E=\frac{(6.626\times {10}^{-34})(3\times {10}^8)}{0.50\times {10}^{-10}}=3.976\times {10}^{-15}J\therefore E=3.98\times {10}^{-15}J$