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PHY 2241 – Physical Science Survey I Lab
Sound and Light Lab (Rev. 4)
Discussion:
Sound and light both travel in waves. Light is a type of transverse wave and does not
require a medium. Sound is a type of longitudinal wave and it does require a medium to
be transmitted. The amplitude is the displacement of the wave from the rest or
equilibrium position. It is essentially the energy carried by the wave. For sound, this is
exhibited as loudness – the greater the amplitude of the wave, the louder the sound.
Sound that is too loud can damage our hearing and cause other physiological effects. The
frequency of a wave is the number of waves that pass a given point per second. It is
measure in units called Hertz. Different frequencies of sound waves are interpreted by
our ears as different pitches if the wave is in the audible range of 20 to 20,000 Hz. Visible
light is part of the electromagnetic spectrum which also includes ultraviolet radiation,
microwaves, radio (and TV) waves, and infrared radiation. We cannot see these because
their wavelengths are out of the range that our eyes can see – shorter than 4 x 10-7 m and
longer than 8 x 10-7 m. (Wavelength is the distance from a point on 1 wave to the
corresponding point on the next wave and can be measured in meters.) Our eyes interpret
wavelengths between these 2 values as visible light of different colors with the shorter
length appearing as violet and the longer length as red. Frequency and wavelength are
related to each other in what we call the wave equation. The equation is:
v = f
where v is velocity, f is frequency and  is wavelength.
For electromagnetic radiation (including light in a vacuum) the velocity is represented by
c, which stands for the speed of light in a vacuum and has a value of 3 x 108 m/s. For
sound in air at 0o C (or 32 oF), the speed is 330 m/s or 1000 ft/sec. As air gets warmer,
the sound travels faster. The speed of sound increases by 0.60 m/s (or 2.0 ft/s) for every
degree about 0oC. The equation for finding the speed of sound at Celsius temperatures
above 0oC is:
v = v0 + 0.60 m/s (T)
where v is the speed at the new temperature, vo is the speed at 0oC which is 330 m/s, and
T is the Celsius temperature.
Motion between the source of a wave and the observer can distort the wave, making it
either longer or shorter and thus changing its frequency. The Doppler effect is the change
in the frequency of wave due to the relative motion between the wave source and the
observer. Sound and light are both subject to the Doppler effect. Most stars look white
or yellow to us. When we view stars through a telescope, we can tell if the star is moving
away from us by the color that it appears. If it appears red, we say that it has a red shift
and we know that it is moving away from us, so the frequency is lowered and the wave is
stretched so that its wavelength is in the red part of the visible spectrum. If a star
appears blue, then the waves are being crunched together because the star is moving
toward us, thus increasing the frequency and reducing the wavelength into the shorter
blue region of the visible spectrum.
Light can be used to produce images on surfaces such a mirrors and lenses, such as inside
our eyes or in microscopes. When light rays hit a flat surface, they bounce off at the
same angle. If they hit a curved surface such as a lens or curved mirror, they either
diverge (get farther apart) or converge (come together and cross). Two types of images
are produced in this way. A virtual image is produced when the rays do not cross. A
virtual image will be upright, but reversed left to right. It cannot be projected onto a
screen. A regular mirror produces one of these .A real image is produced when the rays
converge. It will be upside down and can be projected onto a screen, such as at the movie
theater. Convex lenses are thicker in the middle and thinner on the edges. Concave lenses
are thinner in the middle (“caved in”) and thicker on the edges. Convex lenses are used in
cameras, microscopes, projectors, telescopes, and some eyeglasses and contact lenses.
Concave lenses are used in some eyeglasses and contact lenses and sometimes in
combination with convex lenses. A concave mirror is a converging mirror that caves in
at its middle. They produce both real and virtual images, depending on the distance from
the mirror. A convex mirror is a mirror that bends out in the middle, such as a shoplifting
mirror that you find in some stores. The rays diverge when they bounce off the surface of
a convex mirror.
Purpose: To explore properties of light and sound.
Materials used: busy street, cardboard or plastic box about the size of a shoe box, at least
3 sizes of rubber bands of approximately the same length but different widths, calculator,
Internet, shiny metal spoon, flat mirror, tee shirt with lettering
Part I – Sound
Procedure:
A. Doppler effect – Find a safe location beside a busy street or interstate highway to
observe. Listen to the sound of a vehicle as it comes toward you, passes you, and then
moves away .Note the change in pitch, not the loudness. Record your observations on the
report sheet.
B. Pitch – Arrange the rubber bands from the thickest to the thinnest. Put the rubber
bands in the same order around the cardboard box so that they are about an inch apart.
Pluck each in order and listen to the pitch. Compare them. Record your observations on
the report sheet.
C. Calculations – see Report Sheet
D. Internet – Hearing Loss Go to the following websites and read the information to help
you answer the questions on the Report Sheet.
(1) http://www.cdc.gov/niosh/topics/noise/ which takes you to the main topic of Noise
and Hearing Loss Prevention. Read through the topics: Facts and Statistics (Fact Sheet:
Work Related Hearing Loss, Occupationally Induced Hearing Loss, Other Resources and
then Heahthy Youth – Noise Induced Hearing Loss) and Hearing Loss Prevention
(preventing Occupational hearing Loss
(2) http://www.osha.gov/SLTC/noisehearingconservation
(3) http://www.asha.org/public/hearing/Hearing-Loss/ and then How We Hear and
Hearing Loss (then Types, Causes, Noise and Noise at Work)
(4) http://www.webmd.com/a-to-z-guides/hearing-loss-prevention
Answer questions on the Report Sheet.
Part II – Light
Procedure:
A. Real and virtual images
1. Hold the bowl of a spoon close to your face (about 2 inches away) and look at your
image. You may have to move it toward or away from you to get it to focus. Answer
questions on the Report Sheet.
2. Move the bowl of the spoon away from you. Your image will go out of focus and the
back into focus as you mo it farther away. Answer questions on the Report Sheet.
3. Hold the spoon close to your face with the bowl facing away from you. You may have
to move it toward or away from you a little to focus it. Answer questions on the Report
Sheet.
4. Put on a tee shirt with lettering on it. Look in a mirror and try to read the words.
Answer questions on the Report Sheet.
B. Optical illusions – Our eyes are easily fooled. This is why vertical stripes tend to make
people look taller and thinner and horizontal stripes make people look shorter and
wider. Optical illusions really illustrate this. Search the Internet to find 1 . Or, go to .
http://kids.niehs.nih.gov/illusion/illusions.htm
Describe 1 of the optical illusions and
record it on the Report Sheet. Have another person look at it (without telling them what
you see) and record his/her observations on the Report Sheet.