Question

In a laser tube all photons:
(A) Have same energy
(B) Have same wavelength
(C) Move in same direction
(D) Move with same speed

Answer 1

Hint A photon is the smallest discrete amount or quantum of electromagnetic radiation. It is the basic unit of all light. As per quantum theory, photons have energy equal to their oscillation frequency multiplied with Planck’s constant. Einstein also proved that light is a flow of photons, Relating to properties you can easily solve this question.

Complete step by step solution
Photons are always in motion and, in a vacuum, travel at a constant speed to all observers of \[2.998 \times {10^8}m/s\] . This is commonly referred to as the speed of light, denoted by the letter c.
Now let’s see some properties of photons:
1. Photons have 0 mass and rest energy. Photons only exist as moving particles.
2. Photons are elementary particles despite lacking rest mass.
3. Photons have no electric charge.
4. Photons are stable.
5. Photons are spin-1 particles which makes them bosons.
6. Photons carry energy and momentum which are dependent on the frequency.
7. Photons can have interactions with other particles such as electrons, such as the Compton effect.
8. Photons can be destroyed or created by many natural processes, for instance when radiation is absorbed or emitted.
9. When in empty space, Photons travel at the speed of light.
Mass of photons decided by:
\[E = m{c^2}\]
So mass will be:
\[m = \dfrac{E}{{{c^2}}} = \dfrac{{hv}}{{{c^2}}}\]
Momentum is given by:
\[p = mc\]
So now we can say from properties that the speed of photons is constant. So option D is correct.

Note The main point of Einstein’s light quantum theory is that light’s energy is related to its oscillation frequency. He maintained that photons have energy equal to “Planck’s constant times oscillation frequency,” and this photon energy is the height of the oscillation frequency while the intensity of light corresponds to the number of photons.