Question

How many photons are in a laser pulse of 0.586 J at 673nm?

a) 2.25 x 10¹⁸
b) 8.72 x 10¹⁹
c) 5.45 x 10²⁰
d) 3.91 x 10²¹

Answer 1

To calculate the number of photons in a pulse, we ascertain the energy of one photon at the given wavelength and divide the total energy of the pulse by the photon's energy. After the calculations, the resulting value is compared with the given options.

Step-by-step explanation:

To determine the number of photons in a laser pulse of 0.586 J at 673 nm, we first need to calculate the energy of a single photon with that wavelength. The energy (E) of a photon is given by the equation E = h*c/λ, where h is Planck's constant (6.626 x 10-34 J·s), c is the speed of light in a vacuum (approximately 3.00 x 108 m/s), and λ is the wavelength of the light (in meters). The wavelength must be converted from nanometers to meters by dividing by 109.

First, convert the wavelength:

• 673 nm = 673 x 10-9 m

Then calculate the energy of a single photon:

• E = (6.626 x 10-34 J·s)(3.00 x 108 m/s) / (673 x 10-9 m)

This gives us the energy per photon. Next, we divide the total energy of the laser pulse (0.586 J) by the energy per photon to find the number of photons:

• Number of photons = Total energy / Energy per photon

After completing the calculations, we can compare the result with the multiple choices provided to identify the correct one.