This document provides an overview of single and double slit experiments. It describes how waves can be transverse, longitudinal, or a combination. Interference occurs when multiple waves interact, which can be constructive or destructive. Diffraction is the spreading of waves when passing through an opening. In a single slit experiment, only diffraction is observed as there is a single wave. In a double slit experiment, both diffraction and interference are observed as two waves interact. The experiment results in a pattern of bright and dark bands due to the constructive and destructive interference between the waves.

1. Single and Double Slit Experiments Overview
In this module, you'll learn about interference and diffraction of
waves.
Objectives:
After completing Module 5 activities, you will be able to:
After completing Module 5 activities, you will be able to:
· Describe the differences between interference and diffraction.
· Describe qualitatively how single and double slit diffraction
gratings produce diffraction patterns.
Assignments:
1. Single and Double Slit Experiments Lab Submission
Key Terms:
· Transverse Wave
· Longitudinal Wave
· Interference
· Diffraction
· Single Slit Experiment
· Double Slit Experiment
Single and Double Slit Experiments Background
In order to fully understand the single and double slit
experiments, the first step is to appreciate what waves are and
why they are important. For the purpose of this lab, there are
two types of waves to consider: transverse and longitudinal:
Transverse and Longitudinal Waves
A simple wave consists of a periodic disturbance that

2. propagates from one place to another. The wave
in Figure (Links to an external site.)propagates in the horizontal
direction while the surface is disturbed in the vertical direction.
Such a wave is called a transverse wave or shear wave; in such
a wave, the disturbance is perpendicular to the direction of
propagation. In contrast, in a longitudinal wave or
compressional wave, the disturbance is parallel to the direction
of propagation. Figure (Links to an external site.) shows an
example of a longitudinal wave. The size of the disturbance is
its amplitude X and is completely independent of the speed of
propagation vw
.
In this example of a transverse wave, the wave propagates
horizontally, and the disturbance in the cord is in the vertical
direction.In this example of a longitudinal wave, the wave
propagates horizontally, and the disturbance in the cord is also
in the horizontal direction.
Waves may be transverse, longitudinal, or a combination of the
two. (Water waves are actually a combination of transverse and
longitudinal. The simplified water wave illustrated
in Figure (Links to an external site.)shows no longitudinal
motion of the bird.) The waves on the strings of musical
instruments are transverse—so are electromagnetic waves, such
as visible light.
Sound waves in air and water are longitudinal. Their
disturbances are periodic variations in pressure that are
transmitted in fluids. Fluids do not have appreciable shear
strength, and thus the sound waves in them must be longitudinal
or compressional. Sound in solids can be both longitudinal
and transverse.
The wave on a guitar string is transverse. The sound wave
rattles a sheet of paper in a direction that shows the sound wave
is longitudinal.
Earthquake waves under Earth’s surface also have both
longitudinal and transverse components (called compressional
or P-waves and shear or S-waves, respectively). These

3. components have important individual characteristics—they
propagate at different speeds, for example. Earthquakes also
have surface waves that are similar to surface waves on water.
Diffraction and Interference
There are two wave properties that are important: diffraction
and interference. Diffraction can be defined as the spreading out
of a wave due to its passing through a small opening. A simple
example of diffraction of light is shown in this image taken
from a student winner of an AAPT High School Physics Photo
Contest (click here (Links to an external site.) to view).
A good visual representation of the process of diffraction
through different gap sizes can be found here (click to
load) (Links to an external site.).
The other property is interference. This occurs when more than
one wave interact at a specific location. The interference can be
constructive (waves in phase such that high intensity regions
align with one another) or destructive (waves out of phase
where high and low intensity regions cancel one another).
The link included here (click the link) (Links to an external
site.) discusses both constructive and destructive interference
for a transverse wave. Time should be spent on this link so that
you are comfortable with exactly what is taking place. This is a
key factor in the double slit experiment, which will be the focus
for the second part of this lab. For further reading on
interference, the following page from Physics Classroom is
recommended (Links to an external site.).
For the single slit experiment, only diffraction is important.
This is because a single wave is spreading out and there is no
overlap. The following link (click to view) (Links to an
external site.)provides a good explanation of diffraction, and
shows how waves combine to form the diffraction pattern.
Fig. : Diffraction from a slit. Above is given the value of the
wavelength of the incident light and the slit width (1 nm = 10-
3 micron). The figure was obtained from applet java: "Single-

4. Slit Diffraction (Links to an external site.)".
(Credit:Sergey Kiselev e Tanya Yanovski-Kiselev
Notice in the image that there is a very bright central maximum
with small oscillations to either side. For the purpose of this lab
we are simply going to concentrate on the strong central
maximum. The brightest part of the image occurs directly across
from the center of the slit (no diffraction … the path of light
has no deviation). Now notice that moving to either side causes
a reduction in light intensity. This can be thought of as a
decrease in intensity as the diffraction angle increases.
For the double slit experiment both diffraction and interference
are important, as now there are two waves that interact with one
another.
Fig: Double slits produce two coherent sources of waves that
interfere. (a) Light spreads out (diffracts) from each slit,
because the slits are narrow. These waves overlap and interfere
constructively (bright lines) and destructively (dark regions).
We can only see this if the light falls onto a screen and is
scattered into our eyes. (b) Double slit interference pattern for
water waves are nearly identical to that for light. Wave action is
greatest in regions of constructive interference and least in
regions of destructive interference. (c) When light that has
passed through double slits falls on a screen, we see a pattern
such as this. (credit: PASCO)
This diagram needs a bit more analysis. Notice the horizontal
line drawn to the right from the midpoint between the two slits.
Follow this line to the right and you see that it is aligned with a
bright region. Moving upward or downward from this bright
region there are several alternating dark and light regions. The
pattern that you see to the far right is then the result of the
constructive and destructive interference.
Note: Some of this material is from OpenStax College Physics.
© Feb 28, 2018 OpenStax. Textbook content produced by
OpenStax is licensed under a Creative Commons Attribution
License 4.0 (Links to an external site.) license.

5. Download for free at http://cnx.org/contents/[email protected]
1) Write at least two full paragraphs summarizing the material
from the introduction. Include anything you learned, had
clarified, or still are unsure about.
2) Graph the following data on standard Cartesian graph paper:
(0.3, -1)
(1.7, -1)
(3, 2)
(4, 0)
(5.7, -1)
(7, 2)
(9, -2)
(10, 0)
(11.7, 1)
(13, -2)
(14, 0)
(15, 2)
(15.7, 1)
(18, 0)
(19, 2)
(20, 0)
3) The horizontal axis is given in cm and the vertical axis is in
mm.
What is the amplitude of this wave?
What is the wavelength of this wave?
Can this single wave display interference?
4) Now consider another wave that has the same amplitude and
the same wavelength. Is it possible to set up these two waves so

6. that there is constructive interference? If so, how?
5) Now, is it possible to set up these same two waves so that
there is destructive interference? If so, tell how and also tell
how much shift total there must be between the constructive
interference in the previous question and the destructive
interference here.
6) Study the following link:
https://plus.maths.org/content/physics-minute-double-slit-
experiment-0
On the following page, write at least two full paragraphs about
wave-particle duality. Include what we see with photons and
what we see with electrons. Do you find this surprising? Can
you suggest why we see this with electrons but would not see it
with, for example, baseballs?
7) What is the difference between energy and intensity as far as
light waves are concerned? How would you change the energy?
How would you change the intensity? Are these changes
independent of one another? Why or why not?

7. 8) Discuss what changes you might expect to see if the energy
of the light wave was changed for the double slit experiment.
Why?
9) Discuss what changes you might expect to see if the intensity
of the light wave was changed for the double slit experiment.
Why?
10) Write at least two full paragraphs to summarize what you
did in this lab. Be sure to include anything you learned, had
clarified, or still don’t understand.