A source of sound produces 20 compressions and 20 rarefactions in 0.2seconds . The distace between a compression and a rerefaction is 50cm . Find the wave length, frequency and time period of the wave.

We know, 20 compression and 20 rarefactions together make 20 complete oscillations of the wave. So, the time period is, T = 0.2/20 = 0.01 s

So, frequency is, f = 1/T = 1/0.01 = 100 Hz

Distance between a compression and a rarefaction is 50 cm. So, distance between two compression or two rarefaction or 1 wavelength is = 2 × 50 = 100 cm = 1 m