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Question
A thin metal plate is placed against the teeth of cog wheel. Cog wheel is rotated at a speed of 120 rotations per minute and has 160 teeth. Calculate:
- frequency of node produced.
- speed of sound, if wavelength is 1.05 m.
- what will be the effect when the speed of cog wheel is doubled?
Solution
Frequency for rotation of wheel = 120 rotations per minute
f = `120/60` rotation per second
f = 2 rotations per second
Number of teeth on the wheel = n = 160
(i) Frequency of nod = nf
f = 160 × 2
f = 320 Hz
(ii) Wavelength = λ = 1.05 m
Speed of sound = v = ?
v = λf
v = 1.05 × 320
v = 336 ms-1
(iii) When speed of cog wheel is doubled, then frequency of nod increases and hence sound becomes shrill.
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