Question

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

Answer 1

Infrared waves whenever encounter any object they cause entire atoms and molecules to vibrate and due to these vibrations, the internal energy and temperature of the object increases. Electromagnetic waves carry energy.

Complete step by step answer:
(a) As we know Infrared waves are discovered by Herschel. The frequency of infrared red waves are $3\times {{10}^{11}}Hz$ to $4\times {{10}^{11}}Hz$. They are produced by hot bodies and molecules.
Infrared waves, with frequencies lower than that of visible light, vibrate not only the electrons, but entire atoms or molecules in the structure of the glass. Their vibration increases the internal energy and temperature of the structure. Which is why Infrared waves are often called heat waves.
Basically they are used in physical therapy to treat a muscular strain. Infrared also provide energy to satellites by using solar cells. They are also used for producing dehydrated fruits.

(b) Basically these waves are discovered by Maxwell. As the electromagnetic waves don’t need a medium to propagate. EM waves are waves which can travel through the vacuum in outer space. EM waves have momentum and this momentum can be transferred to the surface on which it occurs.
The Electromagnetic waves carry energy. It means that they also carry momentum and exert radiation pressure.
The energy and momentum transported are not continuously distributed over the wave front. Energy and momentum are transported by photons in discrete packages.

Note:
When electromagnetic waves hit the body the mass is lost by this momentum is conserved i.e. transferred from electromagnetic waves to the body.