Udit Gupta Ex-VMC Physics Faculty
WELCOME TO THE 7H LESSON IN WAVES. The sub-topics include: Beats & Doppler's effect and 1 numerical. Visit: unacademy.com/plus to register for SPECIAL CLASSES.
BEATS AND DOPPLER'S EFFECT When two waves of nearly equal (but not exactly equal) frequencies travelling with same speed in the same direction superpose on each other, they give rise to beats. Beat frequency: It is defined as number of beats heard per second. Beat frequency No. of beats s-1 (2 ) difference in frequencies.
BEATS AND DOPPLER'S EFFECT When a source of sound or an observer or both are in relative motion, there is an apparent change in the frequency of sound as heard by the observer. This phenomenon is known as Doppler's effect.
BEATS AND DOPPLER'S EFFECT According to Doppler's effect the apparent frequency heard by the observer is given by: Here Vs, Vo and v are speed of source, observer and sound relative to air. The upper sign on Vs (or Vo) is used when source (observer) moves towards the observer (source) while lower sign is used when it moves away.
NUMERICAL4 In figure, a source of sound of frequency 510Hz moves with constant velocity Vs 20m/s in the direction shown. The wind is blowing at a constant velocity vw 20m/s towards an observer who is at rest at point B. The frequency detected by the observer corresponding to the sound emitted by the source at initial position A, will be (speed of sound relative to air is 330m/s) (a) 485Hz (b) 500Hz (c) 512Hz (d) 525Hz 30 lw
SOLUTION 4 Apparent frequency, v+v (v + vw v,cos60) 510 (330+ 20) 330 20 20cos60 350 - 510 x525Hz 340 Correct option is (d)
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A Mechanical Engineer from NIT Allahabad here to help learners with physics. Also a Star ⭐ educator.