Question

According to photon theory of light which of the following physical quantities associated with a photon do not/does not change as it collides with an electron in vacuum:
A. Energy and momentum
B. Speed and momentum
C. Speed only
D. Energy only

Answer 1

Hint:According to the photon theory of light, photons carry energy with frequency and carry constant speed and momentum with wavelength. Photons can be easily created and destroyed.

Formula used:
The energy of a photon is given as,
\[E = h\upsilon \]
Where, h is the Planck's constant and \[\upsilon \] is the frequency of the photon.
\[p = \dfrac{h}{\lambda }\]
Where,\[\lambda \] is the wavelength of the photon.

Complete step by step solution:
According to the photon theory of light, a photon is a discrete bundle or quantum of electromagnetic or light energy. Photons are always in motion in a vacuum and have a constant speed of light to all observers. Its value is given as \[3 \times {10^8}m/{\mathop{\rm s}\nolimits} \].

As we know, the energy of a photon is given as,
\[E = h\upsilon \]
And the momentum of the photon is given as,
\[p = \dfrac{h}{\lambda }\]
In a vacuum according to the photon theory of light, photons carry constant speed and momentum with wavelength so it is not applicable.

Hence option A is the correct answer.

Note: Photon is a light particle which was drawn up by Einstein. The main point of this quantum theory of light is that light energy is related to the frequency as this frequency is equal to the speed of light divided by its wavelength. Quantum theory tells us that light is composed of particles that are known as photons and also that matter is composed of particles like electrons, protons and neutrons.