Wave questions II

Consider the musical note G, 392 Hz.  Find the following:

1.  The frequencies of the next two G's, one and two octaves above.

2.  The frequency of the G one octave lower than 392 Hz.

3.  The frequency of G#, one semi-tone (piano key or guitar fret) above this G.

4.  The frequency of A#, 3 semi-tones above G.
5.  The wavelength of the 392 Hz sound wave, assuming that the speed of sound is 340 m/s.

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 6.  Describe the Doppler Effect.

 7.  An ambulance (emitting a 1000 Hz tone) approaches you and then passes you.  Describe the tone heard in these situations.  Give answers as 'greater than 1000 Hz', 'equal to 1000 Hz', or 'less than 1000 Hz.'

 a.  What tone does the ambulance driver hear as they approach you?
b.  What tone do you hear as the ambulance approaches you?
c.  What tone does the ambulance driver hear after they pass you?
d.  What tone do you hear after they pass you?


Note that I will not ask you to perform the calculation on a test, but rather just set it up.

Answers:

1.  392 x 2 = 784 Hz; 392 x 4 = 1568 Hz

2.  392/2 = 196 Hz

3.  392 x 1.0594 = 415 Hz

4.  392 x 1.0594 x 1.0594 x 1.0594  (or 392 x 1.0594^3) = 466 Hz

5.  wavelength = speed / frequency = 340/392 = 0.87 m

 6 and 7 - see class notes.

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