Characteristics of Waves:

1. Wavelength ( ) : The distance between two consecutive crests or trough is known as wavelength,

It is denoted by  (lambda). Its SI unit is metre (m).

Smaller units are also used like centimetre (cm), nanometer (nm), micron ( ), angstrom (A⁰), picometer (pm).

1m = 10⁹ nm = 10¹⁰ A = 10¹² pm

2. Frequency ( ): The number of waves that passes a given point in one second is known as the frequency.Its SI unit is hertz (Hz or s^-1)

3. Time period (T): Time taken by the wave for one complete cycle or vibration is called time period.

Unit= second per cycle

4. Velocity (v): It is the distance travelled by a wave in one second.The velocity of light is simply written as ‘c’.

Velocity = Frequency x Wavelength

c =vλ

SI unit = ms^-1

5. Wave Number ( ): It is the reciprocal of the wavelength that is no. of waves present in 1 meter. It is denoted by the symbol  (nu bar). Its SI unit is m^-1.

v=1\λ

PLANCK’S QUANTUM THEORY:

According to planck’s quantum theory:

(1) The energy emitted or absorbed by a body not continuously but discontinuously in the form of small discrete packets of energy and these packets are called quanta.

(2) In case of light, the smallest packet of energy is called as ‘photon’.

(3) The energy of each quanta is directly proportional to frequency of the radiation i.e.

h is proportionality constant or Planck’s constant

h=6.626 x 10^-31 kJ s    or         6.626 x 10^-34 J s           or         6.626 x 10^-27 erg s

(4) Total amount of energy transmitted from one body to another will be some integral multiple of energy of a quanta.

where n is an integer and it is principle quantum number