# Electromagnetic radiation and its characteristics

When an electrically charged particle is accelerated alternating electric and magnetic fields are produced and transmitted. These fields are transmitted in the form of waves and called Electromagnetic waves of electromagnetic radiation.

### Important characteristics of a wave

Velocity : It is defined as the linear distance travelled by the wave in one second.

Units : cm $sec^{-1}$ (0r) m $sec^{-1}$

All kinds of electromagnetic waves have the same velocity.

$(3&space;\times&space;10^{8}&space;m&space;\;&space;sec^{-1}&space;or&space;\;3\times&space;10^{10}&space;cm&space;\;&space;sec^{-1})$

Wavelength (λ) : It is defined as the distance between any two successive crests or troughs of a wave.

Units: A ; m ; cm; nm or pm 1 = $\AA$ = $10^{-10}$ m

$1&space;\;nm&space;=$$10^{-9}&space;\;m$ $=$ $10^{-7}$$cm$

$1&space;\;pm&space;=$ $10^{-12}\;&space;cm$

Frequency ($\nu$) :

It is defined as the number of waves passing through a point in one second.

Units : Hertz (Hz) ; cycles $sec^{-1}$ or $sec^{-1}$

$\nu&space;=&space;\frac{c}{\lambda}$

Wave number ($\bar&space;\nu$):

It is defined as the number of waves present in one unit length. It is equal to the reciprocal of the wavelength.

$\bar&space;\nu$ $=$ $\frac{1}{\lambda}$ $=$ $\frac{\nu}{c}$

Relation between wavelength and frequency :

$c&space;=&space;\nu\times&space;\lambda$

$\therefore$ $\nu&space;=&space;\frac{c}{\lambda}$