Question

A laser produces red light of wavelength 632.8 nm. Calculate the energy,

Answer 1

Answer:

189.2 KJ

Explanation:

Data Given

wavelength of the light = 632.8 nm

Convert nm to m

1 nm = 1 x 10⁻⁹

632.8 nm = 632.8 x 1 x 10⁻⁹ = 6.328 x 10⁻⁷m

Energy of 1 mole of photon = ?

Solution

Formula used

                     E = hc/λ

where

E = energy of photon

h = Planck's Constant

Planck's Constant = 6.626 x 10⁻³⁴ Js

c = speed of light

speed of light = 3 × 10⁸ ms⁻¹

λ = wavelength of light

Put values in above equation

                   E = hc/λ

                   E = 6.626 x 10⁻³⁴ Js ( 3 × 10⁸ ms⁻¹ / 6.328 x 10⁻⁷m)

                   E = 6.626 x 10⁻³⁴ Js (4.741 x 10¹⁴s⁻¹)

                  E = 3.141 x 10⁻¹⁹J

3.141 x 10⁻¹⁹J is energy for one photon

Now we have to find energy of 1 mole of photon

As we know that

1 mole consists of  6.022 x10²³ numbers of photons

So,

     Energy for one mole photons = 3.141 x 10⁻¹⁹J x  6.022 x10²³

     Energy for one mole photons = 1.89 x 10⁵ J

Now convert J to KJ

1000 J = 1 KJ

1.89 x 10⁵ J = 1.89 x 10⁵ /1000 = 189.2 KJ

So,

energy of one mole of photons = 189.2 KJ