Question

A sound wave of frequency 400 Hz is travelling in air at a speed of 320m/s. 

1. The speed of sound wave in vaccum is______ 

• 320m/s more than 
• 320m/s less than
• 320m/s Zero 

2. What is the wavelength of the above wave? 

3. Calculate the difference in phase between two points on the wave 0.2m apart in the direction of travel.

Answer 1

1. Zero

2. v = fλ
λ = \(\frac{v}{f}\) = \(\frac{320}{400}\) = 0.8m

3. At 0.2 m apart, the phase difference’is given by

∆Φ = 0.20.8×2π = \(\frac{π}{2}\)rad.