To Determine the wavelength of sodium light using plane transmission grating :Practical

Aim : To Determine the wavelength of sodium light using Plane transmission grating.
Apparatus : Diffraction grating, Spectrometer , Source of monochromatic sodium light, prism etc.
Formula :        

 where,

 λ _{- Wavelength of Sodium Light}

 (a + b) _{- Grating element which is given by}                      

                  _{(a+b)=2.54/15000}

 _{θn - Angle of diffraction for order n}

    n  - Order of spectrum

Diagram : 

Grating producing Central Maxima

First order diffraction spectrum Produced by grating

Procedure : 

1) Keep the Grating on prism table of the spectrometer and observe the Principal Maxima through telescope.

2) Rotate the telescope on either side(R.H.S.) of Principle maxima, the first order maxima will be observed. Measure the angle from W1 and W2.

3) Rotate the telescope again on same side so that the second order  maxima, will be observed. Measure the angle from W1 and W2.

4) Rotate the telescope on other side of Principle maxima, the first order maxima will be observed identical with the first observed maxima. Measure the angle from say W1' and W2'.

5) Rotate the telescope again on same side (i.e other side L.H.S) so that the second order  maxima from other side will be observed. Measure the angle from say W1' and W2'.

6) Calculate the first order and second order maxima with the help of observation table.

7) Now Calculate the wavelength of Sodium Source for first order and second order maxima.

Observation Table :

  

Order of spectrum	Window No.	RHS Spectrum (P)				LHS Spectrum  (Q)				Angle of Diffraction
		MSR	VSR	VSRX LC	TR	MSR	VSR	VSRX LC	TR	(P~Q)/2
I	W1
	W2
II	W1
	W2

Result :  The  Wavelength of Sodium Source is  _____ .

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.