b . They do not need a medium to travel . That means they can even travel in vacuum .
Characteristics of electromagnetic radiations :
a . Wavelength : It may be defined as the distance between two neighboring crests or troughs of wave as shown . It is denoted by λ .
b . Frequency ( ν ): It may be defined as the number of waves which pass through a particular point in one second .
c . Velocity ( v ): It is defined as the distance travelled by a wave in one second . In vacuum all types of electromagnetic radiations travel with the same velocity . Its value is 3 X10 8 m sec -1. It is denoted by v
d . Wave number : Wave number is defined as the number of wavelengths per unit length .
Velocity = frequency x wavelength c = νλ Planck ' s Quantum Theory-
o The radiant energy is emitted or absorbed not continuously but discontinuously in the form of small discrete packets of energy called ‘ quantum ’. In case of light , the quantum of energy is called a ‘ photon ’
o The energy of each quantum is directly proportional to the frequency of the radiation , i . e . E α υ or E = hυ where h = Planck ’ s constant = 6.626 x 10 -27 Js
Energy is always emitted or absorbed as integral multiple of this quantum . E = nhυ Where n = 1,2,3,4 ,.
Black body : An ideal body , which emits and absorbs all frequencies , is called a black body . The radiation emitted by such a body is called black body radiation .
Photoelectric effect : The phenomenon of ejection of electrons from the surface of metal when light of suitable frequency strikes it is called photoelectric effect . The ejected electrons are called photoelectrons .