Electromagnetic Radiation: General Considerations

 Introduction

A radiation is basically the energy emitted in the form of wave (light) or particle (photons). Electromagnetic radiation (EMR) is the energy which flows through the space or any medium in the form of EM waves.

 

EMR is formed due to the oscillating electric and magnetic fields at the right angle to each other. 

 Image from  weather.gov

The overall direction of movement of the wave is perpendicular to the direction of oscillating electric and magnetic fields. The radiation composes of energy packets called as photons.

 

 

General fundamentals                  

Amplitude is the distance from the medium of wave to the maximum vertical displacement, in short- the height of the wave. The more is the amplitude, the more will be energy of the wave or vice versa. 

Wavelength refers to the distance associated with the one complete cycle of oscillation. It can be from one crest to other crest or one trough to next trough. The more the wavelength, the lesser will be the frequency and hence energy. It is measured in metres, centimetres, micro meter.

Frequency refers to the number of complete oscillation cycles per second. Its units are Hertz (Hz). The more is the frequency of the wave, the greater will be the energy associated with it.

Wave number refers to the number of waves per centimetre (cm). It is measured in cm^-1 or kayser.

 

Types of Electromagnetic waves:

Based on the differing wavelengths and frequencies of the waves, Electromagnetic spectrum composes of following different types of waves:

TYPE OF WAVE	WAVELENGTH
Cosmic rays	10-9 nm
Gamma rays	0.2 –1 Angstrom (A)
X- Rays	1- 10 A
Ultraviolet Radiation	200 -400 nm
Visible Radiation	400- 800 nm
Infrared Radiation	2.5 – 25 µ
Microwaves	0.1 – 100 cm
Radio Waves	1 – 1000 m

 

A general diagram showing the applications of different types of EM Waves is given in Figure 1.3 below.

 Image from imagine.gsfc.nasa.gov

 

Types of transitions in various regions of EM spectrum are:

 

Electromagnetic Region	Type of transition
X- Ray	Bond- breaking
UV/Visible	Electronic
Infrared	Vibrational
Microwave	Rotational
Radiofrequency	Nuclear spin (NMR), Electronic spin (ESR)