Question

A laser emits light that has a frequency of 6.69 x 10¹⁴ s-1. If the laser emits a “pulse” (a burst of light) that contains 7.0 x 10¹⁷ photons, what is the total energy of that pulse in Joules?

Do not use scientific notation in your answer. Give the answer ( in Joules) to 2 significant figures.

Answer 1

This problem can be done using the planks law that is , E = N*h*v , here in the given equation the variables are ,N which is the total number of photons , h is the planks constant (6.626 * 10^-34 Js^-1) and v is the frequency. Now the values of each of the variables in the equation are ,

Frequency of laser , v = 6.69 * 10¹⁴ s^-1

Number of photons present in the laser beam , N = 7 * 10¹⁷

E = N*h*v

E = (7 * 10¹⁷ ) * ( 6.626 * 10^-34 Js ) * (6.69 * 10¹⁴ s^-1 )

E = 3.102 * 10^-15 J

E = 3.102 fJ ( fJ = femto joule , 1fJ = 10^-15J)