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Waves

Question
CBSEENPH11026303
Wired Faculty App

A sound source producing waves of frequency 300 Hz and wavelength lm observer is stationary, while source is going away with the velocity 30 m is, then apparent frequency heared by the observer is

  • 270 Hz

  • 273 Hz

  • 383 Hz

  • 300Hz

Solution

B.

273 Hz

An increase (or decrease ) in the frequency of sound, light or other waves as the source and observer move towards (or away from) other. The effect causes the sudden change in pitch noticeable in a passing siren, as well as the redshift seen by astronomers. 

Here source is moving and the observer is stationary so according to Doppler effect we use the following relation.

Apparent frequency n' = n VV + Vs

  V = Velocity of sound

  Vs = velocity of source

  ∴   n' = 300 332332 + 30

           = 273 Hz

Some More Questions From Waves Chapter

When two tuning forks (fork 1 and fork 2) are sounded simultaneously, 4 beats per second are heard. Now, some tape is attached on the prong of the fork 2. When the tuning forks are sounded again, 6 beats per seconds are heard. If the frequency of fork 1 is 200 Hz, then what was the original frequency of fork 2?

The sound waves after being converted into electrical waves are not transmitted as such because

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