explain doppler's effect in reflection of sound (echo) and also explain condition with derivation ?
Answers
Answer:
Explanation:
Sound: Doppler Effect and Echo
Sound is a form of energy. It is that form of energy which makes us hear. Sound wave is a vibratory disturbance in a medium which carries energy from one point to another without there being a direct contact between the two points. According to Doppler Effect the frequency of sound wave changes with motion, either of the source or of the observer. The reflection of sound wave is called echo. It varies in different mediums.
By SHIKHA GOYAL MAR 11, 2016 16:32 IST
Sound is a form of energy. It is that form of energy which makes us hear. Sound wave is a vibratory disturbance in a medium which carries energy from one point to another without there being a direct contact between the two points. Doppler Effect is an everyday experience. It is observed that the pitch of the sound is higher when we approach a stationary source of sound with high speed. And if we moved away from the source of sound the pitch becomes lower. This change in the pitch (frequency) of a wave due to motion of the source or observer is called Doppler Effect.
Johann Christian Doppler, an Austrian physicist first proposed Doppler effect in 1842.
Jagranjosh
The three situations under which frequency changes:
Case 1: Source moving, observer stationary
Let us choose the direction from the observer to the source as positive direction of velocity. Suppose the source (S) is moving with velocity (vs) and the observer and medium are at rest or stationary. Now, let the speed of wave at angular frequency and period (To), which is measured by the observer at rest in that medium be v. Let us assume that the observer has a detector which counts every time a wave crest reaches it.
Now at time t = O the source is at point S1. The distance between source and observer at this point is L. At this point source emits a crest which reaches the observer at time t1 = L/v. Now at time t = To the source moves a distance vsTo and reaches at point S2. Th distance between observer and point S2 is L + vsTo. At point S2 the source emits second crest which reaches the observer at:
t2 = To + (L + vsTo)/ v
At time n To, the source emits (n+1)th crest and this reaches the observer at time:
Tn+1 nTo L ns To/v
Hence in a time interval
nTo L nvs To/v L/v
the observer’s detector counts n crests and observer record period of the wave as T given by
T nTo L nvsTo/v L/v/n
=To+ vs To/v
= To (1+vs/v)
This equation can be rewritten in terms of the frequency vo:
v = vo (1+vs/v)-1
If vs is small compared with the wave speed v, then
v = vo (1-vs/v)
We replace vs with - vs, to get
V = vo (1 + vs/v)
Therefore, the observer notices higher frequency when the source approaches near him and lower frequency when the source moves away from him. .
