Question

Two trains, one coming towards and another going away from an observer both at $4 \mathrm{~m} / \mathrm{s}$ produce a whistle simultaneously of frequency $300 \mathrm{~Hz}$. The number of beats heard by observer will be (velocity of sound = $340 \mathrm{~m} / \mathrm{s}$ ) (A) 5 (B) 6 (C) 7 (D) 12

Name: Problem 87, Chapter 9: A Complete Resource Book in Physics for JEE Main
Uploaded: 2021-10-11T13:24:51-08:00
Duration: 2 min 35 s
Channel: Dheeraj Sharma
Description: Two trains, one coming towards and another going away from an observer both at 4 m / s produce a whistle simultaneously of frequency 300 Hz. The number of beats heard by observer will be (velocity of sound = 340 m / s ) (A) 5 (B) 6 (C) 7 (D) 12

   Two trains, one coming towards and another going away from an observer both at $4 \mathrm{~m} / \mathrm{s}$ produce a whistle simultaneously of frequency $300 \mathrm{~Hz}$. The number of beats heard by observer will be (velocity of sound = $340 \mathrm{~m} / \mathrm{s}$ )
(A) 5
(B) 6
(C) 7
(D) 12

A Complete Resource Book in Physics for JEE Main

Sanjeev Kumar 1st Edition

Chapter 9, Problem 87

Instant Answer

Solved by Expert Dheeraj Sharma

10/11/2021

Step 1

We have to find the number of beats heard by the observer. The frequency of the whistle is given as 300 Hz and the velocity of sound is 340 m/s. The velocity of the train is given as 4 m/s. Show more…

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Two trains, one coming towards and another going away from an observer both at $4 \mathrm{~m} / \mathrm{s}$ produce a whistle simultaneously of frequency $300 \mathrm{~Hz}$. The number of beats heard by observer will be (velocity of sound = $340 \mathrm{~m} / \mathrm{s}$ ) (A) 5 (B) 6 (C) 7 (D) 12

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Key Concepts

Doppler Effect

The Doppler Effect refers to the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the source of the wave. In acoustics, this effect is observed when either the source of sound or the observer is moving, leading to a perceived increase in frequency if they are moving closer together, or a decrease if they are moving apart. It is essential for understanding how motion affects the sounds heard by an observer.

Beat Frequency

Beat Frequency is the phenomenon that occurs when two sound waves of slightly different frequencies are superimposed, producing a new wave whose amplitude modulates at a frequency equal to the absolute difference between the two original frequencies. This effect is commonly used in tuning musical instruments and in various applications in acoustics to measure small differences in frequency.

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