Study of Double Refraction by Quartz Prism- Write Up : Practical- BE II SEM - ADVANCED PHYSICS

Aim : To Determine the Principle Refractive Index for Ordinary and Extra-Ordinary Ray when refraction takes plalce through Quartz Prism.
Apparatus : A Source of Sodium Light, Spectrometer , Spirit level, Quartz Prism.
Formula : 
                

 where,

 μ_{o - RI for o-ray}

 μ_{e- RI for e-ray}

 _{δme - Angle of minimum deviation for extra ordinary ray}

  δmo - Angle of minimum deviation for ordinary ray

      A  - Angle of Prism

Diagram : 

(a) Ray Diagram

(b) Measurement of angle of Prism

(c)  Measurement of angle of minimum deviation

Procedure : 

A) Leading of Spectrometer

1) Base of the spectrometer is to be leveled with the help of screws provided at the bottom of the spectrometer using spirit level.

2) The axis of telescope , collimeter and prism should be adjusted.

3) The axis of rotation of telescope should be vertical.
B) Measurement of Angle of Prism

1) Make the arrangement as shown in figure (b)Place the Prism on Prism table so that its refracting edge A is at the center of table and rough surface BC parallel to the ground lines on the Prism table. The light falls symmetrically on both the faces AB and AC.

2) Turn the telescope towards the face AB to receive reflected image and taken it on cross wire. Note down the reading say W1 and W2.

3) Turn the telescope towards the face AC to receive reflected image and taken it on cross wire. Note down the reading say W1' and W2'.

C) Measurement of Angle of minimum deviation

1) Make the arrangement as shown in figure (c). Bring the rough side of prism on either left or right side of prism table.let it be on right side of prism table. 

2) Observe the direct ray from telescope without any deviation from the original position. Focus the direct ray with the help of the telescope  to receive double refracted image and taken it on cross wire. Note down the reading say W1 and W2. 

3) Turn the telescope towards the rough face of prism to receive deviated image either o or e ray. Receive first deviated image o-ray from direct ray and taken it on cross wire. Note down the reading say W1' and W2'.

4) Now turn the telescope towards the right side to receive the second deviated image say e-ray. Receive second deviated image e-ray from direct ray and taken it on cross wire. Note down the reading say W1'' and W2''.

Observation Table :   

Window No.	Reflection from face AB (P)				Reflection from face AC (Q)				Angle of Prism (Mean)
	MSR	VSR	VSRX LC	TR	MSR	VSR	VSRX LC	TR	(P~Q)/2
W1
W2

Table (1)  Measurement of Angle of Prism

Window No.

Direct Ray (P)

Ordinary Ray

Extra-Ordinary Ray

Angle of Minimum Deviation (Mean)

MSR

VSR

VSRX LC

TR

MSR

VSR

VSRX LC

TR

MSR

VSR

VSRX LC

TR

Direct ray ~ (Ordinary/Extra- ordinary ray)

W1

W2

Table (2) Measurement of Angle of minimum deviation

 Result :  The Principle Refractive Index for ordinary and extraordinary rays for Quartz Prism are _____ and_____ respectively.

Precautions :

1) Slit should be narrow and bright

2) The axis of telescope , collimeter and prism should be horizontal.

3) Both windows vernier scales should be set so that the error due to rotation of telescope should be eliminated.