Modern Physics: Momentum of Photon

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The momentum of a Photon

Photons have momentum even though they don't have mass
We came up with an equation that describes the total energy of the particle squared is equal to the rest mass energy squared plus the momentum times the speed of light whole squared.

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This equation did give us the momentum of any kind of particle which is moving at any velocity
So how does that deal with or works for a photon? Well, a photon has no mass, when we are dealing with photon we can say that mass 'm(ph)' = 0 and of course them traditional sense of momentum we know that momentum is equal to the mass times velocity i.e. p = mv.
So we know that if the particle does not have momentum but that is actually not the because with the given equation if we assume that rest mass (m0) of the particle is zero. m0 = 0 then

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That is a very interesting part, where a particle has no mass actually has a momentum which means that for example if there an electron and a photon is incident on the electron or hits the electron actually makes the electron move.
So the final result is that the electron will be pushed off to the side by the momentum of the photon.
Now let's say that we have a photon that has a wavelength λ = 505nm.
Now if we have to calculate the momentum of the photon.

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The momentum of a light beam

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Consider a LAZER turned on for one second and then turned off. The beam of light emitted for the travels a distance of 3x10e8 meters as light travels 3x10e8 meters in 1 second.
It is called the one-second PULSE and the pulse will cover 3x10e8 meters distance
Now we have to find the momentum of that beam of light.
The power is 1.5mW.
The wavelength is 626nm of the light beam of light.
To find the no. of photons to find the momentum of light.

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Physics Handwritten Notes