Why ambulance have different siren sounds?

          Doppler Effect with Ambulance Sound

            Lets imagine you are walking with a little crowed road.Suddenly, you hear the distant wail of a siren of an ambulance.The siren of ambulance sounds with a high pitch and louder as it approaches towards you.And when it moves away from you the sound is less pitch. This effect of the sound is due to the Doppler Effect.

             Doppler effect refers to the change in wave frequency during the relative motion between a wave source.It was discovered by Christian Johann Doppler.It works on both light and sound objects.For instant, when a sound object moves towards you, the frequency of the sound waves increases, leading to a higher pitch. Conversely, if it moves away from you ,the frequency of the sound waves decreases and the pitch comes down. The drop in pitch of ambulance sirens as they pass and the shift in red light are common examples of the Doppler effect.

Other applications of Doppler effect:-

•  Doppler effect is used to measure the speed at which stars and galaxies are approaching or receding from us, in a mechanism named red shift,or blue shift.
• A device named Acoustic Doppler Current Profiler (ADCP) is a hydroacoustic current meter similar to a sonar,used to measure water current velocities over a depth range using the Doppler effect of sound waves scattered back from particles within the water column.
• An Echocardiogram that produce an accurate assessment of the direction of blood flow and the velocity of blood and cardiac tissue at any arbitrary point using Doppler effect.
• Used as a siren in a emergency vehicle to reduce the accident in road.