Question

a) Why are infrared waves often called heat waves? Explain.
b) What do you understand by the statement,” Electromagnetic waves transport momentum”?

Answer 1

Hint: Infrared rays are sometimes also called infrared light. It is that part of the electromagnetic spectrum which is not visible to us human eyes. Infact, only light is that part of the electromagnetic spectrum which is visible to us. Any other radiation, whose wavelength doesn’t fall under the category of visible light, like radio waves, microwaves, etc. is either not visible to us or visible under special conditions.

Complete step by step answer:
Heat waves are those waves which carry heat along with them. The wavelength of infrared waves are sufficient to set atoms and molecules into vibrational motion. Hence whenever an object is encountered with infrared waves, produces heat due to the vibrations of atoms.
This is the reason why infrared waves are called heat waves.
Electromagnetic radiation like light consists of photons which are discrete packets of energy. These particles when falls onto a surface exerts a pressure on the surface called the radiation pressure. The amount of momentum can be calculated by using the De-Broglie hypothesis. According to the hypotheses, the momentum of a radiation of wavelength ‘$\lambda$’ equals $p=\dfrac{h}{\lambda}$in magnitude.

Note:
The wavelength of infrared radiation is greater than that of visible light. In fact students must have an idea of the frequencies and wavelengths of different types of electromagnetic waves. Let’s see a pneumonic to remember the frequencies of electromagnetic radiation.

This could be remembered as “ Raoult's Mother Is Visiting Uncle Xavier’s Garden “.
The arrow below shows the increase in Frequency of the electromagnetic waves on moving from left to right.