Sound is a form of energy It is that form of energy which makes us listening Sound wave is a vibratory disturbance in a medium which carries energy from one point to another without a direct contact between the two points. Doppler Effect is a daily experience It is seen that the pitch of the sound is high And if This change in the frequency of a wave due to the resolution of the source or observer is called Doppler Effect.
Johann Christian Doppler, an Austrian physicist first proposed Doppler effect in 1842.
Uses of Doppler Effect
Used by police
At airport to guide aircraft
In military to detect enemy aircraft
Doctors use Doppler Effect to study heart beats and blood flow
Echo
If stand in an empty hall and say something then after a while We will hear our own voice in the form of echo
When the sound is repeated due to the reflection of sound waves, it is called echo. Soft surface absorbs sound So, it is when the sound is reflected from a hard surface like tall brick wall or a cliff, we hear echo
Calculation of minimum distance to hear an echo
There is a time interval of 1 / 10th of a second or more for a human So we can hear the original sound and reflect sound only if there is a time-interval of at least 1 / 10th of a second or 0.1 second.
Our distance from the sound reflecting surface should be 17.2 meters in order to hear an echo in air at a temperature of 20 degrees. This distance will change as the temperature changes. Thus, echo will be more on hot day
The minimum distance to hear a echo in water should be 75 meters.
Uses of echo :
To measure depth of sea
To locate underwater objects
To investigate inside human body
