Hello It Is not clear to me how would be possible to calculate the energy possessed by a single photon or if you prefer how do one calculate the wave lenght of a single photon?
To my knowledge (since mass and speed are constant in photons right?) The energy of a photon depends only on it’s frequency (or the wave lenght of course) but I Just don’t understand how the frequency of a single photon can be calculated? Or how the wavelenght info can be extracted from a single wave (in this case electromagnetic wave)?
Please help.
In: 1
Photons do not have mass in the traditional sense like we are used to, that is the rest mass that objects that do not move have. The rest mass of photons is zero.
The speed of photons is constant or more exactly constant in a vacuumm , that is c.
Energy is equivalent to mass, the famous formula E=mc^2 shows the connection between mass and energy. In relativity, the relativistic mass is the rest mass and mass that is added because of energy.
Photons only have relativistic mass and it is not constant
E=mc^2 is not the complete formula, it on only valid for objects that do not move The complete formula is E^2 = =(pc)^2 + (m0c^2)^2 where p is the momentum and m0 is the rest mass.
The rest mass m0 of a photon is zero so only the formula E^2 =(pc)^2 => E= pc
Photons have momentum and move at a constant speed but have no rest mass.
The relationship between energy and frequency is
E= hf where h is Planck constant and it is the frequency
Because frequency = sped/ wavelength you can also use.
E=hc/λ where λ is the wavelength.
You can use it with E= pc => p=E/c and get
p=E/c =(hc/λ)/c)=h/λ
To calculate one you can just plug in the known value you have and calculate the other.
If you talk about measuring the energy of a single photon there there are ways. The angle of visible light bends when it changes medium depending on the wavelength, this is why rainbow and prism split up light. Let the split light then hit a sensor, the location is dependent on the wavelength. So we can measure the weight of a single photon but notice where it hits the sensor.
An instrument that do this is called a https://en.wikipedia.org/wiki/Spectrometer
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