Question

How do you calculate the momentum of a photon?

Answer 1

Hint: Momentum is defined as the mass in motion. It is a vector quantity and has both magnitude and direction. If the object’s velocity changes, the momentum also changes. It is the inertia of translation motion.

Complete step by step answer:
Momentum is also called translational momentum or linear momentum and is defined as the product of the mass of the particle and its velocity. It depends on the frame of reference and is a conserved quantity which indicates that in a closed system, the momentum is not affected by the external forces and thus the total linear momentum also does not change.
The quantum of the electromagnetic field including the electromagnetic radiation like light and radio waves is the photon and it is a type of elementary particle.
The photons can be destroyed as they will undergo absorption while traveling through the matter.
By using the Broglie equation, we can calculate the momentum of a photon. Mathematically it is given by,
$p = \dfrac{h}{\lambda }$where h, is the Planck's constant and $\lambda $is the wavelength of the light.
Thus substituting the values of $\lambda $ and h, we get,
$p = \dfrac{{6.6 \times {{10}^{ - 34}}}}{{4.5 \times {{10}^{ - 7}}}} = 1.47 \times {10^{ - 27}}$
Thus the momentum of a photon is $1.47 \times {10^{ - 27}}$kilograms meters per second.

Note:
1. Humans can directly see the photons as the human eyes are designed to detect the light.
2. Photon is massless and it travels at the speed of light. Gamma rays have the highest energy. Gamma rays are a form of nuclear and cosmic Electromagnetic radiation and thus will have the highest frequencies.
3. Jean Buridan discovered momentum.