2. Michelson’s Interferometer
Albert Abraham
Michelson
An American physicist
known for his work on
measuring the speed of
light and especially for
the Michelson–Morley
experiment. In 1907 he
received the Nobel
Prize in Physics
3. PRINCIPLE OF INTERFERENCE
Super position of two coherent light waves
Two sources are
coherent if
1. Same frequency
2. Same amplitude
3. In phase
4. 1. Wavelength of sodium vapour lamp using
Michelson’s Interferometer
Aim:
To find the wavelength of sodium vapour lamp
using Michelson's interferometer
Apparatus required:
Michelson’s interferometer, condensing lens
and a pin hole.
Formula:
The wavelength of sodium lamp is λ=
2𝑑
𝑁
metre
10. III. White light Fringes
Fringes are observed only when the path
difference is small.
After about 10 fringes a number of colours
overlap. So only the first few coloured
fringes are visible.
Used In the determination of zero path
difference especially in the standardisation
of the metre.
11.
12. PROCEDURE
The distance of the mirrors M1and M2 are adjusted to be
very nearly equal from the glass plate G.
A thin sheet with a pointer in it is placed in between the
source and the glass plate G. If we look into the telescope, four
images of the pointer will be seen. The screws behind the mirror
M2 are adjusted till the images coincide. Now the two paths are
exactly equal.
The field of view will be totally dark. A slight motion of M1
parallel to itself will produce the circular interference fringes by
shifting the mirror M2 practically straight.
These fringes are called Haidinger fringes. The conditions
for interference maxima are fulfilled.
13. DETERMINATION OF WAVELENGTH
Adjust the mirror to obtain circular fringes. Note
the reading of the position of the mirror M1 on the pitch
scale, head scale and field of view are counted. Then
reading is taken again for 10 fringes.
The procedure is repeated to get consistent
values. The distance d is calculated for the shift of 10
fringes . The mean values are taken to calculate the
wavelength of sodium light.
14. Where, d is the distance moved by the screw for the
shift, of N- fringes in m
Observation:
• Pitch of the drum = 1 mm
• No of division on drum = 100
• Least count of drum (1/100) = 0.001 cm
• Pitch of the head scale = 0.001 cm
• No of division in head scale = 100
• Least count of head scale (0.001/100) = 0.00001 cm
15. Order of Fringes Scale reading cm Distance moved
(d) for 10 fringes
(m) x 10-4
λ=
2𝑑
𝑁
x 10-7m
n 10.08726 - -
n + 10 10.08758 3.2 6.4
n + 20 10.08789 3.1 6.2
n + 30 10.08819 3.0 6.0
n + 40 10.08847 2.8 5.6
n + 50 10.08840 3.3 6.6
n + 60 10.08912 3.2 6.4
n + 70 10.08937 2.7 5.4
n + 80 10.00896 3.0 6.0
n + 90 10.08996 2.7 5.4
n + 100 10.09026 3.0 6.0
16. Order of
Fringes
Scale reading
cm
Distance
moved (d) for
10 fringes(m)
x 10-4
λ=
2𝑑
𝑁
x 10-7m
n + 110 10.09058 3.2 6.4
n + 120 10.09087 2.9 5.8
n + 130 10.09117 3.0 6.0
n + 140 10.09151 3.4 6.8
n + 150 10.09182 3.1 6.2
n + 160 10.09211 2.9 5.8
Mean 6.0625x 10-7m
Result: The Wavelength of sodium lamp λ= 6.0625x 10-7m
17. 2. wavelength of He-Ne laser using Michelson’s
interferometer
Aim: Determining wavelength of He-Ne laser using Michelson’s
interferometer
Apparatus Required:
He –Ne laser, Microscope objective, screen, etc.
Formula: λ=
2𝑑
𝑁
metre
Where, d- Distance moved by the screw in metre of the shift for N
number of fringes.
18. PROCEDURE
• Set the Michelson interferometer on lab table with
coarse adjustable knob pointing towards you.
• Set the lab jack in front of microscopic objective
holder and set the height using lifting knob.
• Place the He-Ne laser source on lab jack, pointing the
source towards the centre of fixed mirror.
• Plug in the laser cord on AC 220 V, 50 Hz socket.
19. • Turn the laser on and adjust the laser beam height using lab jack
lifting knob until the beam is approximately parallel with the top of the
interferometer and strikes the fixed mirror in the centre.
• Set the viewing screen just opposite of the adjustable mirror M2 to get
the laser beam field view. (Viewing screen should be placed at 1-2 m
from the adjustable mirror to get better resolution).
• To get circular fringes, M1 should be exactly perpendicular to M2. In
this position, Michelson interferometer is said to be in normal
adjustment. The setting needs that the plane of BS exactly bisects the
angle (45°) between the polished surfaces of M1 and M2.
• Using coarse adjustment knob makes the distance of M1 and M2 from
BS nearly equal.
20. • When the laser beam will be passing through beam splitter at 45 ° and
observed in the direction M2, four spots of the He-Ne laser beam are
seen on the viewing screen; two of which are faint and two are
intense. The faints spots are due to reflection from un-silvered surface
of BS and then from M1 and M2 respectively. The intense spots are due
to reflection from silvered surface of BS and M1 and M2.
• The tilting screws at the back of M1 and M2 are adjusted to obtain only
two images. This happens only when the mirror M1 and M2 are exactly
perpendicular to each other.
• Now place the microscope objective in microscopic holder.
• Adjust the height of the microscopic objective so that clear circular
fringes are obtained on viewing screen.
• Make adjustments of mirrors M1 and M2 using top tilting screws to
obtain concentric circular fringes in the viewing screen.
21. Determination of wavelength of He-Ne laser
• The circular fringes are obtained as explained above.
• Move the mirror M2 using fine adjustment knob. The fringes appear or
disappear in the field of view (always move the knob in one direction for
precise measurement).
• Note down the reading of coarse adjustment knob. Let it be `m´. Multiply this
reading with least count 0.01 mm.
• Take the reading of fine adjustment knob. Let it be `n´. Multiply this reading
with least count 0.0001 mm.
• Add the above two readings of coarse and fine adjustment knobs. Let it be L1.
• Rotate the fine adjustment knob to count the number of fringes appearing or
disappearing. Let it be N.
• Note the observations. Let it be L2.
• Subtract L1 from L2 to get the value of d for m fringes.
• Use the formula to calculate the value of d.
23. Order of Fringes Scale reading 𝑳 𝟏
(cm)
Distance moved (d)
for 10 fringes (m) x
10-4
λ=
2𝑑
𝑁
x 10-7m
n 0.9357 - -
n + 10 0.9384 3.3 6.6
n + 20 0.9415 3.1 6.2
n + 30 0.9446 3.1 6.2
n + 40 0.9478 3.2 6.4
n + 50 0.9512 3.4 6.8
n + 60 0.9540 2.8 5.6
n + 70 0.9572 3.2 6.4
n + 80 0.9604 3.2 6.4
n + 90 0.9636 3.2 6.4
24. Order of
Fringes
Initial reading
(cm)
Distance
moved (d) for
10 fringes (m) x
10-4
λ=
2𝑑
𝑁
x 10-7m
n + 100 0.9667 3.1 6.2
n + 110 0.9698 2.8 6.2
n + 120 0.9632 3.4 6.8
n + 130 0.9660 2.8 5.6
n + 140 0.9769 3.1 6.2
n + 150 0.9822 3.1 6.2
n + 160 0.9851 2.9 5.8
Mean 6.3090x 10-7m
Result: The wavelength of He-Ne laser= 6.3090 x 𝟏𝟎−𝟕m
25. REFERENCE
II MSc Non Electronics Lab Manuel – Department of Physics
Sarah Tucker College ( Autonomous) , Tirunelveli -7
Google Images
YouTube Links
https://www.youtube.com/watch?v=nWXT2H0KbZc
https://www.youtube.com/watch?v=lzBKlY4f1XA
https://www.youtube.com/watch?v=jB7suji-fCY
https://www.youtube.com/watch?v=1Qc-HIml-U4
![MICHELSON’S INTERFEROMETER
Albert Abraham
Michelson
(1852 –1931)
Associate Professor in Physics
SARAH TUCKER COLLEGE [AUTONOMOUS]
TIRUNELVELI-627007](https://image.slidesharecdn.com/michelsoninterferometer-200904182909/85/Michelson-interferometer-1-320.jpg)
