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:

1. frequency of node produced.
2. speed of sound, if wavelength is 1.05 m.
3. what will be the effect when the speed of cog wheel is doubled?

Answer 1

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.