Please help with this question... Problem 30.46 A laser produces a 5.30 mW beam

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Please help with this question...

Problem 30.46

A laser produces a 5.30 mW beam of light, consisting of photons with a wavelength of 623.8 nm .

Part A

How many photons are emitted by the laser each second?

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Part B

The laser beam strikes a black surface and is absorbed. What is the change in the momentum of each photon that is absorbed?

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Part C

What force does the laser beam exert on the black surface?

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Problem 30.46

A laser produces a 5.30 mW beam of light, consisting of photons with a wavelength of 623.8 nm .

Part A

How many photons are emitted by the laser each second?

n = photons/s

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Part B

The laser beam strikes a black surface and is absorbed. What is the change in the momentum of each photon that is absorbed?

p =   kgm/s  

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Part C

What force does the laser beam exert on the black surface?

F =   N  

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Explanation / Answer

h - Planck's constant
c - speed of light (in meters per second)
lambda - wavelength in meters

a) Energy of one photon E = hc/lambda = 6.626 * 10^-34 * 3 * 10^8 / 623.8 * 10^-9
Number of photons = 0.036/(energy of one photon) = 0.036 / 3.188521962 * 10^-19 = 1.129049774 * 10^17

b) p = h/lambda ( change in momentum of each photon)

p = 1.062840654 * 10^-27 Kg m/s

c) Ft = change in momentum of all the photons = change in momentum of each photon * number of photon
  

Ft = change in momentum of all the photons = 1.0628 * 10^-27 * 1.129049774 * 10^17

Ft = change in momentum of all the photons = 1.2 * 10^-10 kg m/s

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