2. ACKNOWLEDGEMENT
First of all, I am deeply thankful to my physics teacher (Rakhi
Maam) for extending her valuable and scholarly guidance
throughout the preparation of this project .I wish to extend my
sincere thanks to Mr. Albert Abraham respected principal of
Montfort Senior Secondary School , for his continuous motivation
and moral support for completing the work. I am also thankful to
all my respected teachers and staff of the school. last but not the
least I am indebted to my friends, classmates and parents for
encouraging and never let me down in my confidence while completing the project
3. CERTIFICATE
This is to certify that JIYA SAINI of Class XII-A
(SCIENCE) of Montfort Senior Secondary school has
completed the research on investigatory project titled “To
study and show diffraction of light ” under the guidance
and supervision of physics teacher (Rakhi Maam) during
the year 2022-2023. The progress of the project has been
continuously reported and has been in my knowledge
4. PREFACE
It is a matter of great pleasure for me to present my investigatory report on topic entitled “
DIFFRACTION OF LIGHT”. During my investigation I came to know about various phenomena
of diffraction of light like about the discovery of diffraction, how did diffraction got it’s name
from, about it’s occurrence, mechanism, types of diffraction, it’s relation with interference and
many more
My investigation included understanding based on real life examples which helped me to
understand the above listed topics easily, as well as some experiments which made me more clear
about the topic
5. WHAT IS DIFFRACTION?
Diffraction is a slight bending of light as it passes around the edge of an object. The amount of bending depends on the relative
size of the wavelength of light to the size of the opening. If the opening is much larger than the light’s wavelength, the bending
will be almost unnoticible
Diffraction refers to various phenomena that occurs when a wave encounters an obstacle or a slit. It is defined as the bending of
light around the corners of obstacle or aperture into the region of geometrical shadow of the obstacle
In classical physics, The diffraction phenomena is described as the interference of waves according to the huygens-fresnel
principle. The characteristic behaviour are exhibited when a wave encounters an obstacle or slit that is comparable in size to
it’s wavelength
DIFFRACTION OCCURS WITH ALL KIND OF WAVES, including sound waves, water waves, electromagnetic waves such as
visible light, rays and radio waves
If we look clearly at the shadow cast by an opaque object, close to the region of geometrical shadow, there are
alternate dark and bright regions, just like in interference.This is just due to the phenomenon of the diffraction,
which is a general characteristic exhibited by all types of the waves
Since wavelength of light is much smaller than the dimensions of most of the obstacles,we do not generally encounter the
effects of diffraction of light in the everyday life observations. However the finite resolution of our eye or of the optical fiber
instruments such as telescopes or microscopes is limited due to the phenomena of diffraction
6. HISTORY OF DIFFRACTION
The effects of diffraction of lights were first carefully observed and characterized by
francesco maria grimaldi who also coined the term diffraction from the latin
diffringere, ‘TO BREAK INTO PIECES’ referring to light breaking up into different
directions.
Issac newton studied these effects and attributed them to inflexion of light rays.
Thomas young performed an experiment in 1803 demonstrating interference from two
closely spaced slits. Explaining his result by interference of waves emanating from the
two different slits, he deducted that light must propagate as waves
7. WHEN DOES DIFFRACTION OCCURS
Diffraction occurs whenever propagating waves encounter changes, its effects are
generally most pronounced for waves whose wavelength is roughly comparable to the
dimensions of the diffracting object or slit. If the obstructing object provides
multiple,closely spaced openings, a complex pattern of varying intensity can result.This
is due to the addition, or interference, of different parts of a wave that travel to the
observer by different paths, where different path lengths result in different phases. The
formalism of diffraction can also describe the way in which waves of finite extent
propagate in free space.
8. MECHANISM OF DIFFRACTION
In traditional classical physics diffraction arises because of the way in which waves
propagate; this is described by the Huygen-Fresnel principle and the principle of
superposition of waves. The propagation of a wave can be visualized by considering
every particle of the transmitted medium on a wave front as a point source for a
secondary spherical wave. The wave displacement at any subsequent point is the sum
of these secondary waves. When waves are added together, their sum is determined by
the relative phases as well as the amplitudes of the individual waves so that the
summed amplitude of the waves can have any value between zero and the sum of the
individual amplitudes. Hence,diffraction patterns usually have a series of maxima and
minima
9. TYPES OF DIFFRACTON
1) SINGLE-SLIT DIFFRACTION : A Long slit of infinitesimal width which is illuminated by light
diffracts the light into a series of circular waves and the wave front which emerges from the slit is a
cylindrical wave of uniform intensit
A slit which is wider than a wavelength produces interference effects in the space downstream of the
slit. These can be explained by assuming that the slit behaves as though it has a large number of point
sources spaced evenly across the width of the slit. The analysis of this system is simplified if we
consider light of a single wavelength. If the incident light is coherent,these sources all have the same
phase.
Light incident at a given point in the space downstream of the slit is made up of contributions from
each of these point sources and if the relative phases of these contributions vary by 2π or more, we
may expect to find minima and maxima in the diffracted light. Such phase differences are caused by
differences in the path lengths overwhich contributing rays reach the point from the slit
10. When the double slit in young’s double slit experiment is replaced by a single narrow slit illuminated by a
monochromatic source, a broad pattern with a central bright region is seen. On both sides there are alternate bright
and dark fringes and regions, the intensity becoming weaker away from the centre.
We can find the angle at which a first minimum is obtained in the diffracted light by the following reasoning. The
light from a source located at the top edge of the slit interferes destructively with a source located at the middle of
the slit, when the path difference between them is equal to λ/2
Similarly, the source just below the top of the slit will interfere destructively with the source located just below the
middle of the slit at the same angle. Along the entire height of the slit, the condition for destructive interference for
the entire slit is the same as the condition for destructive interference between two narrow slits a distance apart that
is half the width of the slit.If light consisted strictly of ordinary or classical particle, and these particles were fired in a
straight line through a slit and allowed to strike a screen on the other side we would expect to see a pattern
corresponding to the size and shape of the slit. However when the single slit experiment is actually performed the
pattern on the screen is a diffraction pattern in which the light is spread out
THE SMALLER THE SLIT,THE GREATER THE ANGLE OF THE SPREAD
12. Both Thomas Young's double-slit experiment and Clinton Davisson and Lester
Germer's electron-beam experiment provided evidence that there is more to the
physical world than classic mechanical properties that can be seen with the naked eye.
These two double-slit experiments revealed that minute particles have unique
mechanical properties. The investigation of these unique mechanical properties gave
birth to the field of quantum mechanics—the condition for quantum behavior being
that a particle must be of low mass or massless as in the case of the photon
13. DIFFRACTION EVENTS
The amount of bending which occurs is based on the wavelength of the light or the
objects size in relation to light's wavelength. In addition to bending, light is sometimes
broken into its basic components. These components are the colors of the rainbow
red,orange, yellow, green, blue, indigo and violet (ROYGBIV).Red light has the longest
wavelength, while violet has the shortest. This is why red is typically the prominent
color in a rainbow and appears to be wider than violet light
Full lunar eclipses permit light waves to bend around the edges of the moon to let the
side facing earth remain visible, albeit an orange- brown color instead of the white
color. This is a due to the distance of the moon from earth,allowing the moon to
completely cover the sun
14. DIFFRACTION AND INTERFERENCE
Diffraction is the bending of waves around an obstacle, while Interference is the
meeting of two waves during the diffraction process and usually happens when there
are two or more slits. Interference of the light waves with each other causes the
diffracted light to become brighter or dimmer during the diffraction process because of
what we call destructive and constructive interference. Also in diffraction and
interference, light energy is redistributed. If it reduces in one region, producing a dark
fringe, it increases in another region producing a bright fringe. Hence there is no gain
or loss of energy which is consistent with the principle of conservation of Energy
16. EXPERIMENTAL ANALYSIS OF DIFFRACTION
SINGLE SLIT DIFFRACTION
AIM: Experiment to study the phenomena of single slit diffraction
REQUIREMENTS: Two razor blade, one glass electric bulb, filter, black paper
PROCEDURE:
1) Hold the two blades so that the edges are parallel and have a narrow slit in between. This can be done easily with
thumb and forefingers as shown in figure, and cover them with black paper.
2)Keep the slit parallel to the filament of the bulb which plays the role of first slit, right in front of eye
3)Adjust the width of the slit andthe parallelism of the edges the pattern the pattern of light and dark bands is visible
4)As the position of the bands(except the central one) depends on the wavelength, they will show some colours
5) Use a filter for red and blue to make fringes clearer, Compare the fringe
17. OBSERVATION: Since the position of all the bands depends on wavelength so they
will show some colour. More the wavelength, More they will diffract.
RESULT: Fringes are wider for red compared to blue
PRECAUTION: Protect your eyes by using spectacles while performing the
experiment. Don’t use sunlight instead of the bulb as sunn produces infrared rays
harmful to our eyes
*By repeating the above experiment with aluminium foil we can easily show double slit
diffraction*
