This document describes Newton's rings, an optical phenomenon where interference patterns of concentric bright and dark rings are observed. It discusses the construction of the experiment using a monochromatic light source, lenses, and a glass plate to create an interference pattern between two glass surfaces. The principle is that constructive and destructive interference occurs between the coherent light rays reflecting off the two surfaces, which vary in distance due to a thin air film. Applications include using the pattern of rings to determine the wavelength of light and refractive index of liquids.

1. NEWTON’S RING
construction, working principle
& its applications
PRESENTED BY-
• AMRITA DAS(ME-127/18)
• SANGYUKTA DAS(ME-157/18)
• RUBIA SULTANA LASKAR(ME-158/18)

2. NEWTON’S RING :
It is phenomenon in which an
interference pattern is created by
reflection of light between two
surfaces – a spherical surface and
an adjacent touching flat surface.

3. Newton’s Ring as observed under
the Microscope

4. CONSTRUCTION:
 A Monochromatic source of light S is kept
at the focus of lens L1.
 The parallel beam of light emerging from L1
falls on the glass plate G kept at 45.
 The glass plate reflects a part of the
incident light vertically downwards
normally on the thin air film enclosed by
the plano convex lens L and plane glass P.
 The reflected beam from the air film is
viewed in microscope. Alternate bright and
dark circular rings with dark spots as centre
is seen.

5. Experimental set-up:

6. Principle Of Newton’s Ring:
 The pattern is formed by alternating pattern of constructive and destructive interference
between the coherent light rays from two surfaces.
 The two pieces of glass make contact only at the centre at other points there is a slight air gap
between the two surfaces increasing the radial distance from the centre to the microscope.
 Light from monochromatic source shines through the top piece and reflects from both the
bottom surface of the top piece and the top surface of the optical flat.
 The reflected rays combine and superpose.
 These rings are concentric.

7. Applications :
 Using the method of Newton’s rings, the wavelength of a given
monochromatic source of light can be determined.
The radius of nth dark ring and (n+m)the dark ring are given by
rn
2 = nRλ and r2
n+m = (n+m) Rλ
rn+m
2 – rn
2 = mRλ
so, λ = [rn+m
2 – rn
2] / Mr
 Using Newton’s rings, the refractive index of a liquid can be
calculated. Let λa and λm represent the wavelength of light in air
and in medium (liquid). If rn is the radius of the nth dark ring in
the air and if rn is the radius of the nth dark ring in liquid, then
rn
2 = nRλa
r`n
2 = nRλm = nRλa/μ
so, μ = rn
2/ r`n
2

8. THANK YOU