Question

Calculate the energy in joule corresponding to light of wavelength 45 nm :
(Planck’s constant h = 6.63 × 10⁻³⁴ Js; speed of light
c = 3 × 10⁸ ms⁻¹)
(a) 6.67 × 10¹⁵
(b) 6.67 × 10¹¹
(c) 4.42 × 10⁻¹⁵
(d) 4.42 × 10⁻¹⁸

Answer 1

Given,

Wavelength of light, λ = 45 nm = 45 × 10⁻⁹ m

Planck's constant, h = 6.63 × 10⁻³⁴ Js

Speed of light, c = 3 × 10⁸ ms⁻¹

The relation between energy, E, and frequency, ν, (from Planck's quantum theory) is given by,

               E = h × ν

                  = $\frac{h × c}{λ}$

                  = $\frac{6.63 × 10⁻³⁴ Js × 3 × 10⁸ ms⁻¹}{ × 45 × 10⁻⁹ m}$

                  = 0.442 × 10⁻¹⁷ J

                  = 4.42 × 10⁻¹⁸ J