(a) The frequencies of infrared waves are lower than the visible light vibrate not only the electrons but entire atoms or molecular of a body. This vibration increases the internal energy and temperature of the structure. That is why infrared waves are often called heat waves. .
(b) We know that, E/m wave transfers energy, but E/m wave also has momentum and this momentum can be transferred to the surface on which it is incident.
Any type of particle or wave thnt is in motion carries momentum either linear or angular, depending on the motion of the partical or wave.
The exact value of the momentum of a wave was given by De Broglie by his equation.
`Plambda = h`
`lambda = h//p` where p = momentum.
