Physics
How does the deviation produced by a prism depend on
(i) the refractive index of its material, and
(ii) the wavelength of incident light
Refraction Plane Surfaces
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Answer
(i) For a given angle of incidence, the prism with a higher refractive index produces 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 since μflint > μcrown
(ii) The refractive index of a given transparent medium is different for the light of different colours. It decreases with the increase in the wavelength of light.
Thus, the refractive index of the material of a prism for visible light is maximum for the violet colour and minimum for the red colour.
Consequently, a given prism deviates violet light the most and red light the least.
(i.e. δ violet > δ red since μviolet > μred )
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Define the term angle of deviation.
A ray of light incident at an angle of incidence i1 passes through an equilateral glass prism such that the refracted ray inside the prism is parallel to its base and emerges at an angle of emergence i2.
(i) How is the angle of emergence 'i2' related to the angle of incidence 'i1'.
(ii) What can you say about the angle of deviation in such a situation?
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(ii) If the angle of incidence is changed to (a) 30°, (b) 60°, state in each case whether the angle of deviation will be equal to less than or more than 36°?