Here we will discuss about electromagnetic wave theory. And what are the important characteristics of wave nature.
What is electromagnetic wave theory
- Maxwell gave the electromagnetic wave theory.
- Energy is emitted continuously in the form of radiations.
- They travel in the form of waves.
- And they are associated with the electric and magnetic fields.
- They are oscillating perpendicular to each other and to the direction of the radiation.
- All of them travel with the velocity of light that is 3 X 10^8 m/s
Characteristics of waves
- Wavelength is the distance between 2 consecutive crests and troughs. It is expressed in 1 A degree = !0^-10m or 10^-8cm, 1 nm = 10^-9m, 1 pm = 10^-12 m
- Frequency is equal to the number of waves passing through a point in one second. Units are hertz or s^-1 ( 1Hz = 1 s^-1 )
- Velocity is distance which the wave travels in 1 second.
- Amplitude is the height of crest or depth of trough.
- Wave number is equal to reciprocal of wavelength.
Electromagnetic Wave Spectrum
It is the arrangement of the electromagnetic radiations in order of increasing wavelength.
Cosmic rays < Gamma rays < X-rays < UV < Visible < IR < Microwaves < Radiowaves
Limitations of Electromagnetic wave theory
This theory was successful in explaining the properties of the light such as interference, diffraction etc.
But it could not explain these 2 phenomenons :
Black body radiation
Black body is a perfect absorber and a perfect radiator of the energy. If the substance heated is a black body then the radiation emitted is black body radiation.
Photoelectric effect
Let the radiation with frequency greater than certain minimum frequency strikes the surface of the metal. It will eject out the electron from the surface of the metal. Work function is this minimum energy.
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