Students first analyse the movement of particles in a medium as a transverse pulse passes.
They then use springs to investigate the speed, phase, reflection, partial transmission and
reflection, superposition and polarization of transverse waves.
Slinky and heavy spring, 2 Masonite boards, 2 polaroid filters Top
2. Longitudinal Waves
Students first analyse the movement of particles in a medium as a longitudinal wave passes.
They look at the displacement of the particles and draw displacement-distance graphs. The
extremes of pressure at compressions and rarefactions are related to the displacements of
the particles. A pressure-distance graph is plotted and compared with the displacement distance
graph.
Students use a ripple tank to investigate propogation, overlapping, reflection from straight
and curved barriers, refraction and diffraction of waves in two dimensions.
Ripple tank and assessories, Rubber hose in the shape of an ellipse, Rubber hose in the
shape of a parabola, 2 blocks approx. 2-3 cm high to raise one side of the tank, Glass sheet
in the shape of a trapezium, Paraffin blocks Top
4. Superposition of Waves
Students use two power supplies, a signal generator, an amplifier/speaker and a CRO to simulate
the superposition of two waves. The principle of superposition is discovered and applied to a
theoretical situation when the waves have slightly different frequencies and would produce beats.
Predictions are made about the beat frequency and the frequency of the note produced by the waves.
This is checked with the equipment. The beat frequency is related to harmony and discord.
The C chord is built up from the first, third and fifth notes C, E and G in the C scale.
Cathode ray oscilloscope, 2 power supplies 2-12 V AC, 3 signal generators, Amplifier with
speaker Top
5. Speed, Frequency and Wavelength of Waves
The equation speed = frequency x wavelength is developed and verified using a ripple tank. Students use a stroboscope to discover that the frequency of waves remains the same when they move into shallow water.
Ripple tank and assessories, Stop watch and metre ruler, Electronic stroboscope, 6 slit disc
stroboscope Top
6. Transverse Standing Waves
Students use superposition to analyse the displacement-distance graphs of two transverse waves
moving through each other. The standing wave nature of the total wave form is discovered. The
theoretical analysis is verified by setting up transverse standing waves in a slinky spring.
A string connected to a vibrating machine is then used to investigate the modes of vibration
of the string.
Vibration machine/motor to shake a string, String, Pulley, 2 G clamps, Base and stem of 50 g
slotted masses, Slinky, 1 meter ruler, Electronic stroboscope Top
7. Longitudinal Standing Waves
Students use superposition to analyse the displacement-distance graphs of two longitudinal waves
moving through each other. The standing wave nature of the total wave form is discovered.
Longitudinal standing waves are observed by setting them up in a slinky spring. The theoretical
frequencies of several modes of vibration of the standing sound waves in open and closed ended
air columns are calculated. Longitudinal standing sound waves are set up in a glass column using
a signal generator and an amplifier/speaker. Resonance is used to check the accuracy of the
theoretical frequencies. Phase changes when sound waves relect from an open ended column and
a closed ended column are investigated.
Glass tube approx. 80 cm long and 5 cm diameter, Cork dust, Signal generator,
Amplifier/speaker, 2 lens holders, Slinky Top
In this experiment students use superposition to discover that a series of sine waves can
superimpose to create a square wave. They connect a signal generator producing square waves
to an interface and the PC displays the component waves they have just superimposed.
By analysing different shaped waves students learn that the fundamental frequency controls the
pitch and the other overtones present control the timbre of a note. They analyse the sounds
made by various musical instruments.
Interface, PC, Signal generator, Sound Wave Analysis kit from Tain Electronics 10 Rowern
Court Box Hill North 3129 Victoria Australia ph fax, Electric Guitar and other musical instruments
available Top
9. Interference of Waves
The theoretical overlap of circular waves from two point sources in phase is analysed.
Equations relating the path difference from each source to the wavelength of the waves are
developed. An interferference pattern is set up in the ripple tank and the no. of nodal lines
related to the wavelength and the source separation. Path lengths are measured and the wavelength
of the waves is calculated. This is compared with a direct measurement using the standing waves
technique. Outside an interference pattern using sound waves from two speakers is set up and the
speed of sound is measured.
Ripple tank, rippler bar and two point sources, Signal generator, 2 amplifier/speakers,
Long extension cord, Tape measure, Large no. of masonite squares approx 5 cm x 5 cm or one
piece of chalk per student if the interference of sound is done on an asphalt or concrete
surface Top
10. Doppler Effect
Students draw scale diagrams of the circular waves moving away from a moving source. The source
moves slower than the waves and the students discover the frequency difference between the waves
ahead and the waves behind the source and develop the formula to calculate the frequency ahead
and behind the source. The source then moves faster than the waves and the students discover the
Mach shock wave and learn how to calculate the angle of the "V". Doppler Effect is then applied
to the light from stars and students learn how to calculate the speed of a star relative to Earth.
