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Standing and Traveling Waves

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Lab Activities

Looks at three wave phenomena: (1) sound pulses, (2) wave trains - traveling waves and (3) standing waves.

In part (1) the speed of a sound pulse in open air is measured using time of flight measurements as described in the "Sound Waves" lab.

In part (2), the wave properties of wavelength, frequency and phase are used to measure the speed of a traveling sound wave in monatomic gas (helium), in a diatomic gas (air) and in a polyatomic gas (carbon dioxide).

In part (3), the following predictions regarding a bounded string system which is being driven by a periodic force, Fcos(wt), are checked:

a. stable waveforms will be seen only when the driving frequency is at or near one of the natural oscillating frequencies of the system;

b. the natural oscillating frequencies are given by the expression

w(n) = (npI/L)((T/m)^.5)

where L is the length of the wire, T is the tension in the wire, m is the linear mass density of the string and n is a positive integer;

c. the speed of the wave is given by v = (T/u)^.5 and that for a given tension the speed of the wave is independent of the oscillating frequency; and

d. for a given tension, the wavelengths of the waves is given by l = nL/2 with nodes at x = l/2, l, 3 l/2, etc and antinodes at x = l/4, 3 l/4, 5 l/5, etc.

Course Level

Introductory: P3, P13, P15

Student Handouts

Equipment

Number of set-ups available:

Per lab station:

Sound pulse setup:

1 2 meter meterstick
1 oscilloscope
4 banana leads
1 microphone/stand
1 speaker/line cord

Traveling wave setup:

1 lucite sound tube
1 oscillator
1 oscilloscope
1 frequency counter
banana leads
BNC cables
BNC to banana lead adaptors
1 balloon

Standing wave setup:

1 oscillator/BNC to banana adaptor (female)
1 frequency counter/BNC cable
1 amplifier
1 black background
4 1 kg masses
2 0.5 kg masses
1 hanger
1 piano wire stretched between 2 right angle posts
2 C-clamps
1 paper towel
2 teflon sleeves
1 magnet
banana leads
2 alligator clips
1 2 meter meterstick
2 ring stands
2 three pronged clamps
2 bar clamps

General class materials:]

1 tank of He gas/regulator and hose
1 tank of CO2 gas/regulator and hose
1 long rubber tube (long enough to reach all stations)
balances with standard mass sets

Sound Pulse

sound pulse apparatus

Travelling Wave

travelling wave apparatus apparatus

Standing Waves

apparatus

Circuit Diagram

circuit diagram

circuit diagram

Notes


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Site contact: largent@Dartmouth.EDU

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