Question:

A source of frequency $240\, Hz$ is moving towards an observer with a velocity of $20\, m/s$. The observer is now moving away from the source with a velocity of $20\, m/s$. Apparent frequency heard by observer, if velocity of sound is $340\, m/s$, is

Updated On: Jul 5, 2022
  • 268 Hz
  • 270 Hz
  • 360 Hz
  • 240 Hz.
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The Correct Option is D

Solution and Explanation

The frequency of the source $v_{0}=240 \,Hz$ The velocity of the source $u _{ s }=+20\, m / s$ (as it moves towards the observer) The velocity of the observer $u _{0}=-20 \,m / s$ (as it moves away from the source) Applying Doppler's effect $v=v_{0}\left[\frac{v+u_{0}}{v-u_{s}}\right]$ $=240 \times\left[\frac{340+(-20)}{340-20}\right]=240\, Hz$
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Concepts Used:

Waves

Waves are a disturbance through which the energy travels from one point to another. Most acquainted are surface waves that tour on the water, but sound, mild, and the movement of subatomic particles all exhibit wavelike properties. inside the most effective waves, the disturbance oscillates periodically (see periodic movement) with a set frequency and wavelength.

Types of Waves:

Transverse Waves -

Waves in which the medium moves at right angles to the direction of the wave.

Examples of transverse waves:

  • Water waves (ripples of gravity waves, not sound through water)
  • Light waves
  • S-wave earthquake waves
  • Stringed instruments
  • Torsion wave

The high point of a transverse wave is a crest. The low part is a trough.

Longitudinal Wave -

A longitudinal wave has the movement of the particles in the medium in the same dimension as the direction of movement of the wave.

Examples of longitudinal waves:

  • Sound waves
  • P-type earthquake waves
  • Compression wave