A source of sound moves towards a stationary observer. Is the increase is pitch due to
(i) increase in the velocity of sound?
(ii) actual or apparent change in wavelength?
(iii) both?

Explanation

When a source of sound moves towards a stationary observver, the incease in pitch is due to actual or apparent change in wavelength, it is so because due to motino of the source of sound towards observer at rest, waves get compressed as the effective velocity of sound waves relative to source becomes less that the actual. As a result of it, the wavelength of sound waves decreases and hence the observed pitch increases.