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.