Basic concepts of electromagnetic spectrum:
1. When Sun light falls on a prism, the transmitted light produces a sequence of colours called 'Spectrum'.
2. A spectrum is a group of wavelengths or frequencies.
3. Colour is a sensation in the brain due to the execution of retina, by an electromagnetic wave of some particular wavelength.
4. The unit of wavelength is Angstrom. It is denoted by Å.
5. 1Å = 10-10m or 10 cm.-8
6. When white light falls on a prism it gives a Spectrum of 7 colours. The seven colours are Violet, Indigo, Blue, Green, Yellow, Orange and Red.
7. Wave length of Violet colour is 4460Å to 4000Å.
8. The radiations having wavelengths less than 4000Å (Violet) are called Ultra Violet radiations (UV).