1. Represented By:
Arijit Dhali

2. Content
 Abstract
 Keywords
 Introduction
 Diffraction
 Interference
 Comparison Chart
 Key Differences
 Conclusion
 References

3. Abstract
In this presentation, our aim is
to distinguish the difference
between diffraction and
interference of light
Throughout this presentation
we will gather the basic
knowledge about the topic .
This presentation is a team
work and every member is
associated with this
presentation has collected the
data from various trusted
sources.

4. Keywords
 Diffraction
 Interference
 Constructive Interference
 Destructive Interference
 Fringes
 Superposition
 Wavefront
 Wavelet

5. Introduction
The crucial difference between diffraction and interference is that diffraction of light occurs
due to the superposition of secondary wavelets that generates from various parts of a wave
front (simply put spreading of light when the beam passes through the slit). As against
interference is the result of the superposition of light waves from 2 coherent sources. Another
important difference between the two is that the intensity of all the bright fringes is not the
same in the case of diffraction however it is same in case of interference. In this session, we
will discuss some other parameters that distinguish the two.

6. Diffraction
 Diffraction is the phenomenon of spreading of the light wave when it passes through a slit
or any small gap.
 But it is noteworthy here that the wavelength of the wave must be comparable with the
dimensions of the slit.
 As in the case of the large opening, the light wave will not bend at the edges. While in case
of smaller opening the bending is quite noticeable.
 But for the very small dimension of the slit, the opening acts as a separate source and thus
allows the spreading of the wave over the entire surface after the slit.

7. Diffraction of Light Waves
Diffraction Pattern

8. Interference
 Interference is the act of superposition of two or more light waves emitted by two
coherent sources travelling in the same medium. We know coherent sources provide a
light wave of the same frequency and constant phase difference.
 So, two waves that are coherent in nature superpose each other when they cross each
other. Thus the superposition of the waves gives algebraic addition of the disturbances
due to separate waves.
 It is to be noted here that the intensity of the resultant wave relies on the amplitude and
phase relation of the two-component waves.

9. Constructive Interference
 When the two superposing waves are of
the same amplitude and phase then the
intensity of the resultant wave will be
higher than the two separate waves.
 More specifically the amplitude of the
resultant wave will be twice the
amplitude of the waves that are going to
be superposed.
 This is called constructive interference.
Destructive Interference
 If the two superposing waves have the
same amplitude but are of opposite
phase then the intensity of the resultant
wave will be lesser than the two
separate waves. The amplitude of the
two waves will be added but as the two
are in opposite phase thus the two
cancels each other.
 This is called destructive interference.

10. Constructive Interference
Destructive Interference

11. Comparison Chart
Basis for Comparison Diffraction Interference
Basic Occurs due to superposition
of secondary wavelets.
Occurs due to superposition
of light waves from two
sources.
Fringe Intensity Not same for all the fringes. Same for all the fringes.
Width of fringes Unequal Equal
Fringe spacing Non-uniform Uniform
Slit or obstacle Required Not required
Direction of wave
propagation
Gets changed after being
diffracted.
Remains unchanged after
getting superposed.
Contrast between maxima
and minima
Poor Good

13. Conclusion
So, from the above discussion, it is clear that interference is the outcome of superposition
while diffraction is the consequence of spreading of the light wave.

14. References
 https://circuitglobe.com/difference-between-diffraction-and-interference.html
 https://en.wikipedia.org/wiki/Diffraction
 https://en.wikipedia.org/wiki/Wave_interference
 Engineering Physics By Dr. Moumita Mukherjee