1. Switch on the electric power supply which is given to He-Ne Laser Apparatus.
   

2. Observe the diffraction pattern on the Screen.
   

3. Measure the distance between grating & the Screen (D).
   

4. For the 1st order spectrum, measure the distance y1 & y2.
   

5. Similarly, for 2nd order spectrum also measure y1 & y2.
   

6. From the available data, compute wavelength (λ) for the given He-Ne Laser light.
   
   

Observation Table

Sr. No.	Order of spectrum(n)	Dist. between Grating & screen in cm(D)	Left (y1) cm	Right (y2) cm	Mean Y = (y1+y2)/2	θ = tan⁻¹ (Y/D)	sin θ	λ = {(a+b) sinθ}/n
1.
2.

Formula

Result

1. Wavelength (λ) of a given light is _____Å
2. Standard value of Wavelength (λ) of a given light is _____Å
3. Percent Error in obtained result _____%