Demonstration of standing waves

Apparatus

Procedure

• Clamp two stands, positioned about 3 m apart, to a bench.

• Place the vibration generator on a laboratory jack or other suitable support, to allow the string plenty of room to vibrate up-and-down.

• Tie the string securely to the hook of a firmly anchored 50 N balance and drape it over the side arm attached to the RHS vertical bar.

• Thread the string through the eye of the vibrator bar – do not tighten the locking screw yet.

• Tension the string to 10 N by tying it securely to the LHS vertical bar.

• Slide the vibration generator as far as practicable to the left and tighten the locking screw.

• Connect the vibration generator to the low resistance output (4 Ω) of the signal generator.

• Turn on the signal generator and select a frequency of 4 or 5 Hz.

• Adjust the output control on the signal generator until the oscillations are visible.

• Slowly increase the frequency until the string vibrates at its fundamental mode.

• Increase the frequency until the first harmonic is visible.

• Continue to increase the frequency to see a series of successive harmonics.

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Demonstration of standing waves

Physics Experiments

Notes

Clamp a loudspeaker (4 Ω or 8 Ω) with its diaphragm facing upwards. Build a column of bluetack taped to the diaphragm as shown.

Raise the loudspeaker and bluetack towards the string so that the string is surrounded and gripped by the bluetack. Connect the signal generator to the loudspeaker. Increase the frequency and observe the standing waves.

Observe longitudinal standing waves in a vertical spring supported from a ceiling hook and with its lower end attached to the vibration generator: note the compression maxima as the applied frequency is increased.

The experiments to investigate the variation of the fundamental frequency of a stretched string with length and tension could be performed using this apparatus.