ÌCSE PHYSICS||Class 10 ||Spectrum||ONE SHOT VIDEO||Chapter-6||

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SPECTRUM FULL CHAPTER (UNIT WISE): SPECTRUM:    • SPECTRUM  

The three factors on which the deviation produced by a prism depends are as follows —

The angle of incidence (i) — As the angle of incidence increases, the angle of deviation first decreases, reaches to a minimum value for a certain angle of incidence and then on further increasing the angle of incidence, the angle of deviation begins to increase.
The angle of prism A — Angle of deviation increases with increase in the angle of prism
Refractive index of the material of prism — For a given angle of incidence, the prism with a higher refractive index produces a greater deviation than the prism which has a lower refractive index.
For example — A flint glass prism produces more deviation than a crown glass prism for same refracting angle.
On increasing the wavelength of light in glass, the speed of light will also increase.

For example — In visible light, the speed of violet colour ( wavelength λ = 4000 Å) is least and red colour (wavelength λ = 8000 Å) is most.

Colour of light is the subjective property of light related to its wavelength.

Different colours differ in their wavelength. In fact, wavelength is the characteristic of colour, irrespective of its origin i.e., the light of the same colour, obtained from different sources will have same wavelength.

The phenomenon of splitting of white light by a prism into its constituent colours is known as dispersion.
All red hot bodies such as a heated iron ball, flame, fire, etc. are the sources of infrared radiations. The Sun is the natural source of infrared radiations.

The electric arc and sparks give ultraviolet radiations. A mercury vapour lamp emits radiations, a part of which has ultraviolet radiations along with the visible light.

The properties of ultraviolet radiations which differ from the visible light are as follows —

(a) They are usually scattered by the dust particles present in the earth’s atmosphere.

(b) They produce fluorescence on striking a zinc-sulphide screen.

Scattering is the process of absorption and then re-emission of light energy by the dust particles and air molecules present in the atmosphere.

In the visible light, the wavelength of red light is longest, therefore the light of red colour is scattered least by the air molecules of the atmosphere.

Hence, the light of red colour as compared to the light of other colours can penetrate to a longer distance without becoming weak.

Thus, red light can be seen from the farthest distance in comparison to the light of other colours having the same intensity.

Hence red light is used for danger signal, so that the signal may be visible from the far distance even in fog, etc.