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3.1 WAVES

P31 008

The following sound waveform was recorded and displayed on the screen of an oscilloscope.

There are six physical quantities that you can calculate from the oscilloscope trace. Given that the speed of sound is 340 m.s^-1, what are these six quantities and their numerical values?

Draw a scaled diagram of an oscilloscope trace recorded by a microphone you would observe for a sound that has double the wavelength and the half the amplitude of the oscilloscope trace shown above.

Picture of an oscilloscope:

View solution below only after you have completed answering the question. The solution is not in a form that you would answer in an examination. The answers are often in more detail to help improve your appreciation and understanding of the physics.

Solution

Knowledge

Travelling harmonic wave

Sinusoidal waveform displayed on oscilloscope

(1)

The recorded amplitude of the trace is A = 10 mV. The amplitude is related to the loudness of the sound wave. The greater the amplitude, the louder the sound.

(2)

The period T is the time for one complete oscillation.

(3)

The frequency f is the number of oscillations per second.

(4)

The angular frequency is

(5)

The wavelength of the sound wave is determined from the speed of sound v and the frequency f of the wave.

(6)

The wavenumber (propagation constant) is

Amplitude halved

Wavelength doubled

Original signal