. REFRACTIVE INDEX OF THE MATERIAL OF THE PRISM AIM To determine the refractive index of the material of a prism using spectrometer. APPARATUS REQUIRED Spectrometer, prism, prism clamp, sodium vapour lamp, spirit level. FORMULA µ = sin sin D (No unit) where, μ → Refractive index of the material of the prism (No unit) A → Angle of the prism (degree) D → Angle of minimum deviation (degree) DIAGRAMS 2A T T Figure (b) Angle of the prism Figure (c) Angle of minimum deviation D T T Figure (a) Angle of the prism Vernier scale Leveling screws Leveling screw of the prism table Slit Collimator Prism Table Eyepiece Telescope Focussing knob XII- - ) XII- - ) - - - - PRACTICAL PROCEDURE ) Initial adjustments of the spectrometer • Eye-piece: The eye-piece of the telescope is adjusted so that the cross-wires are seen clearly.
• Slit: The slit of the collimator is adjusted such that it is very thin and vertical. • Base of the spectrometer: The base of the spectrometer is adjusted to be horizontal using leveling screws. • Telescope: The telescope is turned towards a distant object and is adjusted till the clear inverted image of the distant object is seen. Now the telescope is adjusted to receive parallel rays.
• Collimator: The telescope is brought in line with the collimator. Collimator is adjusted until a clear image of the slit is seen in the telescope. Now the collimator gives parallel rays. • Prism table: Using a spirit level, the prism table is adjusted to be horizontal with the three leveling screws provided in the prism table.
) Determination of angle of the prism (A) • The slit is illuminated by yellow light from sodium vapour lamp. • The given equilateral prism is placed on the prism table in such a way that refracting edge of the prism is facing the collimator. • The light emerging from the collimator is