Electromagnetic Radiation 

Most of the energy which travels via the space is by the electromagnetic radiation. electromagnetic radiation are used for several purposes such as for cooking( sunlight which is used for cooking or solar cooker and microwave), the X-rays  used by the doctors or dentists, the radio waves used by the by doctors in order to make MRI maps of  the body tissues etc are some of the best examples of the electromagnetic radiation. The waves of the electromagnetic rations are characterized by frequency, speed and wavelength.

Almost all our information in astronomy is obtained by the electromagnetic radiation traveling from the object to the observer. Apart from those few objects within the solar system that we have been able to inves­tigate directly, cosmic rays, neutrinos and, in due course, gravity waves are the only other information carriers likely to tell us about the universe as a whole. The electromagnetic radiation wave consists of a magnetic wave and electric waves whose directions are orthogonal, and which vary sinusoidally. The frequency of the sinusoidal variation is called the fre­quency of the wave and denoted usually by ν. The sep­aration of successive crests or troughs gives the wavelength, A. The product of ν and λ gives the wave's velocity. In a vacuum this has a constant value, denoted by c, of 299 792 500 m s"'.

λ ν = c.

In other media the velocity is reduced from c by an amount given by the refractive index, m, of the material:

ν = x / μ

Since even materials normally regarded as opaque have a less than infinite absorption, light penetrates them to a certain extent and so they have a refractive index. We can thus talk, for example, about the velocity of light in a brick!

Questionnaire:

• What is electromagnetic radiation?
• Explain more about the uses of electromagnetic radiation?