Question

A laser emits light that has a frequency of 6.69 x
10^{14} s-1. If the laser emits a “pulse” (a burst of
light) that contains 7.0 x 10^{17} 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 * 10^{14}
s^{-1}

Number of photons present in the laser beam , N = 7 *
10^{17}

E = N*h*v

E = (7 * 10^{17} ) * ( 6.626 * 10^{-34} Js ) *
(6.69 * 10^{14} s^{-1} )

E = 3.102 * 10^{-15} J

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

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