Wave Nature of Electromagnetic Radiation
- Electromagnetic wave theory states that energy is emitted from a source when it is heated this energy is emitted continuously in the form of radiations.
- These radiations associated with an electric and magnetic field which are perpendicular to one another.
Limitations of Electromagnetic Wave Theory
Electromagnetic wave theory was unable to explain:
- Black Body Radiation
- Photoelectric effect
Black Body Radiation
An ideal black body is a perfect absorber and emitter of radiations.
- Phenomena of ejection of an electron from a metal surface when the light of suitable frequency falls on the metal surface.
- The minimum frequency which is required to eject an electron is called threshold frequency.
- The kinetic energy of the emitted electron is directly proportional to the frequency but independent of intensity.
- The number of ejected electrons depends on the intensity of light.
- According to Einstein energy of the photon is equal to the work function and kinetic energy.
A ray of white light splits into a series of colour bands is called a spectrum.
There are two types of the spectrum:
- Emission spectra
- Absorption spectra
After absorbing energy atoms or molecules get excited and when they come back to its ground state they emit certain radiations which produce emission spectra. It is further of two types:
Splitting of white light into seven colours after passing through a prism.
After heating a substance at low-pressure light is emitted which on passing through a prism non-continuous spectrum is obtained. Where coloured lines are separated by dark bands.
When a beam of white light is passing through a chemical substance the spectrum having a dark line.
1/λ = RZ2(1/n12 – 1/n22)
λ is the wavelength of the photon
Wavenumber = 1/wavelength
R = Rydberg’s constant (109677)
Z = atomic number of the atom
n1 and n2 are integers where n2 > n1.