Which of the following statements is false?

Name: Exam Paper Generator | JEE NEET Paper Generator | Vedclass
Brand: Vedclass
Rating: 5 (35 reviews)

Question

(D) $1$. The wavelength of sound is defined as $\lambda = v/f$. Since the source determines the frequency $f$ and the medium determines the speed $v$,

Vedclass · Accepted Answer

When only the medium moves from the source to the observer,the frequency heard by the observer will be greater than the original frequency.

Vedclass · Answer

(D) $1$. The wavelength of sound is defined as $\lambda = v/f$. Since the source determines the frequency $f$ and the medium determines the speed $v$,the wavelength is independent of the observer's motion. Thus,statement $A$ is true.$2$. When the source moves,the distance between successive wave crests changes,which directly affects the wavelength. Thus,statement $B$ is true.$3$. If the medium moves with velocity $u$,the speed of sound relative to the ground becomes $v' = v \pm u$. The wavelength also changes to $\lambda' = (v \pm u)/f$. Since $f$ is constant,the ratio $\lambda'/v' = 1/f$ remains constant,meaning they change in equal proportion. Thus,statement $C$ is true.$4$. When the medium moves from source to observer,the effective speed of sound increases to $v' = v + u$. The frequency heard by the observer is $f' = v'/\lambda$. Since $\lambda = v/f$,we get $f' = (v+u)/(v/f) = f(1 + u/v)$. This is greater than $f$. However,in the Doppler effect,if the source and observer are at rest relative to the ground,the frequency heard is $f' = (v+u)/((\lambda)) = (v+u)/(v/f) = f(1+u/v)$. Wait,the frequency heard by a stationary observer from a stationary source when the medium moves is actually the same as the original frequency because the number of waves passing per second remains constant. Therefore,statement $D$ is false.

Similar Questions

$A$ source of sound of frequency $500 Hz$ is moving towards an observer with velocity $30 m/s$. The speed of sound is $330 m/s$. The frequency heard by the observer will be .... $Hz$

If a source emitting waves of frequency $f$ moves towards an observer with a velocity $v/4$ and the observer moves away from the source with a velocity $v/6$,the apparent frequency as heard by the observer will be ($v =$ velocity of sound).

$A$ policeman on duty detects a drop of $10\%$ in the pitch of the horn of a moving car as it crosses him. If the velocity of sound is $330 \, m/s$,the speed of the car will be ..... $m/s$.

$A$ boy is walking away from a wall towards an observer at a speed of $1\, m/s$ and blows a whistle whose frequency is $680\, Hz$. The number of beats heard by the observer per second is (Velocity of sound in air $= 340\, m/s$).

Vedclass Test Series

Exam Paper Generator

Online Exam Module