W ave P rope rties
Apparatus:
coil springs (stinky of about 1O-cmdiameter and coil spring of about 2.5-cm diameter)
thread
stopwatch
(a) Transversewaves cause the mediumto vibrate at right anglesto the wave motion.
(b)
to the wave motion.
itudinalwaves causevibration
The wave characteristicsyou will observeat this time are commonto all waves.There are not separate
characteristicsfor soundwaves, light waves,water waves,and other kinds of waves. In general,all waves
follow the same rules.Becausethis is so, you can work with waves in a coiledspringto leam about wavesin
general.
Duringthis investigationyou will have an opportunity to becomefamiliarwith some of the major
characteristicsof wave motion. To do this in an orderly manner,each characteristicwill be outlined clearly in
the procedurealongwith any instructionsyou might needin order to observethem.
Recordyour observationsin the spacesprovided.
A. Tranwerse and LonqitudinalWaves
Haveyour lab partner hold one end of the springand stretch it alonga smooth floor until it is about 4 m
long. Practiceshakingyour end of the springsidewaysuntilyou are able to send a clear pulsealong its
length. Severalpulsestogether will form a transversewave train. Notice the direction in which the
pulsestravel and the direction in which the coils of the springmove.
1 . In a tranwerse wave the particlesof the mediumvibrate
(in the same, perpendicularto the) direction in which the wave travels.
2.
3.
of transversewavesare
Otherexamples
wavesand
Reacha short distancedown the spring'slength and gather the coilstoward you and then quicklyrelease
them. The pulsethat travels alongthe spring is a longitudinalpulse.
In a longitudinalpulsethe particlesof the mediumvibrate
(in the same,perpendicular
to the) directionin which the wave travels.
B. The Speedof all Wavesof the SameKindin a GivenMediumarethe Same
Generatea transversepulsein the coil.Keepthe stretch of the coil constant. Estimatethe speedof the
pulse in the medium.Generatea secondpulsebut make it largeror smallerthan the previouspulse.
Comparethe speedsof the pulses.lf you are undecidedyou might try timing the pulsewith the stopwatch.
Try to generate a pulsethat travels along the spring at a different speed.
(the same, different).
4. The speedsof different pulsesin a panicular mediumare ---C. Wavelenqthand Frequencv
Shakethe spring back and forth rapidlyto generatewavetrains in the spring.The wavelengthof a wave
in the spring is the distance from a crest on one side of the spnngto the next crest on the same side. The
frequenry of the wave is the sameas the frequenryat whichyou shakethe spring. Try shaking the spring
regularlybut slowly and then regularlybut rapidly.Observethe wavelengthsof the waves.
5.
6.
7.
8.
Higherfrequencywaveshave
Low frequency waves have
(long,short)wavelengths.
(long, short) wavelengths.
lf groupsof pulsesforrnwavesandthe speedof allthe pulsesyou generatedin the coil arethe samethen
(the same,different).
the speedof allthe wavesgeneratedin the coil shouldbe
The speedof any wave in any mediumis equalto the frequencyof thewavetimesits wavelength(v = flv).
All the waves that you generated in the spring travel at the samespeed.Doesit follow from these two
facts that high frequency waves must have short wavelengthswhile lorryfrequency waves must have long
wavelengths? -----
D. The lnterferenceof Waves
You and your partnercan practicesendingpulsestowardseachother at the sametime. Try this and
closely observethe pulseswhen they come together and alsoafter they passthrough one another. Try
pulsesof the sameand different shapes.Senda pulsedown one sideof the springwhileyour partner sends
a pulsedown the otherside. What happenswhen they meet?
(add up, are the sameas one
9 . When two pulsesmeet in the springtheir displacements
displacement).
10. Whentwo pulsesof about equaldisplacementsapproacheachother from different sidesof the spring
they----(add up, cancel)while they meet.
1 1. After the pulsespassthrough one anotherthey are----(changed,unchanged).
E. ReflectedWaves
Haveyour partner hold one end of the springvery rigidly.Senda pulseto the rigid end and observethe
reflected pulse.
12. A pulse reflected from a rigid medium is reflected -----(right side up, upsidedown).
Nowtie a long thread to one end of the spring.Haveyour partnerholdthe thread and send a pulsetovvard
the end supportedby the string.
13. A pulse reflected from a mediumless rigid than the one in which it has been traveling is reflected
(right side up, upsidedown).
F. WaveTransferralFrom One Mediumto Another
Connectthe slinky with the other coil spring.Stretch the slinky as before. Haveyour partner hold the
end of the springand you hold the end of the slinky.Try sendingpulsesand short wavesdown eachspring.
Observetheir behaviorat the boundarybetweenthe two springs.Observehow a wave changesas it passes
from one mediuminto the other.
14. Eachtime a wave reachesthe boundarybetween the two springsit is-----(partially,
(partially, totally) transmitted.
totally) reflected and
(the same,different).
15. Whena wave entersa new mediumits speedis
(the same,different).
is
16. Whena wave entersa new mediumits wavelength
rt
Name
:-
Period
2. Give examplesof other transversewav€s.
3. Comparethe direction of particle motion to the direction of wave mo
tion in a longitudinal wave.
B. The Speed of All Waves of the Same Kind in a Given Mediuu
{. Describe the speeds of pulses of different amplitudes and different
frequencies in a given medium.
5. Compare the speeds of waves of different amplitudes and frequencies,in a given medi"m.
)
C..Frequencyand Wavelelgtb
6. Comparethe wavelenethsof waveswith higherfrequencieswith the
wavelengthsof waves with lower frequencies
D. The lnterferencc of Wrvcr
7. Describe the magnih.rdeof the displacementwhen two pulsesin
phasemeet in the spring.
8. Describewhat happenswhen two pulses of equal amplitudeand
. 18Ooout of phase meet in the spring.
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9. What happensif the two pulsesare in phase?
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10. Describe the pulsesafter they pass through each other.
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fromProceclure
D.
this diagramusingyourobservations
Figure25-2.Complete
E. Reflected Waves
11. How does reflection of a wave from a rigid barrier affect its phase?
Figure 25-3. Completethis diagramusing your observationsfrom ProcedureE.
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a
Name
Period
12. Reflectionof a Pulsefrom a less rigid mediumhas what affect on
--ii'frffi
,
F. ltave Transferral from One Medium to Another
13. Describewhat happensto a wave when it reachesthe boundarv
betw'eenthe two springs.
14. Frbm your observationof one mediumchange.what do you think
might happento the speedof a wave when it entersa new medium?
.
15. What happens to the wavelength of a wave when it enters a new
medium?
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16. What happens to its frequency?
Interpretcrtion
1. How do your observations in SectionsB and C support the wave
equation in which v = fl?
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2. Summarizethe major characteristicsof wave motionvouobserved
in this investigation.
3. Where in your environment can you observe some of the general
properties of wave motion?
5.
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Figure 25-,1.Us€ thi3 diagramto answerquestionstl-10.
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Name
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Period
e results of wave g_..g3{
For Questions .l_"SJy"_o_v€"_q
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a. when they meet
.1. a.
5. a.
b.
6. e.'
b.
7. c,
b.
8. a.
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b.
b. when they poss one onother.
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9. [n Questions4-8
a. tn which diagnamsdo the pulsesproduce constructiveinterferencewhen thevmeet?
?
(_Jb. [n which diagramsdo the waves producedestructiveinterference?
4-8, in whichdiagramsare nodestonmedas the pulses
10. In Questions
passthroughone another?
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