OPTI 380A Lab 4 Wave Motion - Procedures 2010-2 - Revision...

Revision 9/15/2010
Optics 380A Wave Motion 1
OPTICS 380A
Lab 4: Wave Motion
Procedures
Be sure to answer questions associated with each section and additional questions before
Appendix A.
Part A: WATER WAVES IN A RIPPLE TANK
Use the ripple tank to create water waves. With reference to Appendix A:
Ripple Tank Experiments, perform Experiment 1 (Reflection) and Experiment 2
(Refraction) and answer the questions in the two experiments. Please consider the
additional procedures listed below for this portion of the lab:
1.) Experiment 1, Part 1: Reflection using a straight barrier
a.) Disregard the Setup section on the bottom of page 11 in Appendix
A. The setup has been done for you.
b.) Add the following steps to the Procedure on page 12 of Appendix A:
7.) Measure the distance between wavefronts of the incident
wave.
8.) Turn off the strobe and observe dark lines parallel to the
barrier. Measure the perpendicular distance between these
lines.
2.) Experiment 1, Part 2: Reflection using a curved barrier
a.) It may be easier to see wave effects without the strobe in this portion of the
experiment.
3.) Experiment 2: Refraction
a.) Disregard the Setup section on the bottom of page 15 in Appendix A. The setup
has been done for you.
b.) A careful adjustment of water level is required to observe the effects properly.
Ask your TA to help if you are having difficulty.
c.) Use a source frequency of about 15Hz.

Revision 9/15/2010
Optics 380A Wave Motion 2
d.) In Part 2, use the flat barriers to form an aperture for the lenses.
e.) Again, it might be easier to see some of the wave effects if the strobe is turned off.

Revision 9/15/2010
Optics 380A Wave Motion 3
Part B: STANDING WAVES ON A VIBRATING STRING
Consider a string of length L fixed at both ends so they cannot move. A
driving force exhibiting SHM of frequency f is applied to the string. The question to
ask is how does the string respond as the frequency of the driving force is changed?
Start by referring to Figures 4.1 and 4.2 of the simplified background. We
define a node as being any point along the string that has a (constant) amplitude of
zero. The ends of the string, being fixed, are therefore always nodes. At the same
time, we define the points along the string having the largest amplitude as
antinodes . It may be seen from the figures that the distance between nodes or
antinodes is one-half the wavelength, ! /2, of the standing wave on the string. Note
that at the lowest frequency of vibration, called the fundamental frequency, 2 nodes
and 1 antinode exist on the string. The string will vibrate at higher frequencies,
called overtones , such that an integer number of half-wavelengths of the standing
wave exist on the string.