Question

How many joules per photon are in light with a wavelength 4.50 x 10^-6 mm?

Select one:

a. 4.42 x 10^-17J/photon

b. 2.26 x 10¹⁶ J/photon

c. 4.42 x 10^-20J/photon

d. 1.35 x 10^-8J/photon

e. 1.35 J/photon

Answer 1

We have to apply the equation of photon energy:

h and c are constants

h is the Planck constant, it has a value of 6.63 x 10 ^-34 J/s

c is light speed, it has a value of 3 x 10 ⁸ m/s

is the wavelenght, it has to be in meters, so the first thing we need to do is to convert milimiters to meters this is done dividing by 1000.

4.5 x 10 ^-6 mm * ( 1 m / 1000 mm) = 4.5 x 10 ^-9 m

Now solve the equation:

E = (6.63 x 10^-34 J * s) * ( 3x10⁸ m/s) / ( 4.5 x 10 ^-9)

E = 4.42 x 10^-17 J

That´s the energy of 1 photon so in the light there´s

4.42 x 10^-17 J / photon