Alaser pulse with wavelength 525 nm contains 4.40 mj of energy. how many photons are in the laser pulse

The laser pulse in this question has a wavelength of . To solve this problem, we first have to calculate the energy of a single photon in the laser pulse. The equation for calculating the energy of a single photon of an electromagnetic wave is where is the speed of light, is planks constant and is the wave length of the photons.

For this problem, , and . We use these values to calculate the energy of the photon as shown below,

Now that we know the energy for a single photon, we will divide the total energy given by the energy of one photon to get the number of photons in the pulse. The number of photons is calculated as shown below,

. There are photons.

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