This document summarizes an experiment on interference fringes using a sodium lamp as a monochromatic light source. Rays from the source were reflected through a plano convex lens and formed circular interference patterns known as Newton's rings on the glass surface. The width of the fringes could be measured using a traveling microscope and used to calculate the wavelength of light from the sodium lamp through a formula accounting for the air gap between the lens and glass surface. The circular fringes resulted from the plano-convex lens shaping the light waves into concentric rings.

1. Experiment no. 1
Presented by-
Group 1
EE Batch 1

2.  In this experiment, we have taken sodium lamp as the monochromatic source.
 By MONOCHROMATIC SOURCE, we mean a light source which emits particle of
particular wavelength and not many wavelengths.
 Intensity of fringes also depend upon the air column between lens and the
base.

3. These are INTERFERENCE fringes of
equal thickness.

4. Some of the pictures of apparatus

5. Overall procedure of the experiment
 SOURCE- The source of light is MONOCHROMATIC light source.
 The rays of light reflects from the glass plate which is adjusted at 45 degree
angle with the horizontal.
 After the reflection rays directly goes through plano convex lens.
 And when the light passes through the lens circular patterns are observed like
rings , hence this experiment is named as Newton’s Ring experiment.

6. The microscope used in the experiment is travelling microscope i.e. it can be
moved from left to right or vice-versa to observe the width of fringe, after which
the formula of finding wavelength is applied. Microscope contains Vernier scale
and Main scale. Both the reading are noted and applied in formula using LEAST
COUNT of the scale.

7. Why the fringes observed are CIRCULAR
in shape?
 Because the lens used in this experiment is Plano-convex lens.