Apparent Frequency:Change in Wavelength

Q.

The wavelength is 120 cm when the source is stationary. If the source is moving with relative velocity of 60 m/sec towards the observer, then the wavelength of the sound wave reaching to the observer will be (velocity of sound = 330 m/s)

1. 140 cm

2. 98 cm

3. 144 cm

4. 120 cm

Q. An observer moves towards a stationary source of sound with a speed (1/5)th of the speed of sound. The wavelength and frequency of the source emitted are λ and f, respectively. The apparent frequency and wavelength recorded by the observer are, respectively,

1. $1.2fand\lambda$
2. $fand1.2\lambda$
3. $0.8fand0.8\lambda$
4. $1.2fand1.2\lambda$

Q. Speed of sound wave is v. If a reflector moves towards a stationary source emitting waves of frequency f with speed u, the wavelength of reflected waves will be

1. $\frac{v-u}{v+u}f$
2. $\frac{v+u}{v}f$
3. $\frac{v+u}{v-u}f$
4. $\frac{v-u}{v}f$

Q. When source and detector are stationary but the wind is blowing at speed , the apparent wavelength ${\lambda }^{\prime }$ on the wind side is related to actual wavelength $\lambda$ by [take speed of sound in air as v]

1. ${\lambda }^{\prime }=\lambda$
2. ${\lambda }^{\prime }=\frac{v_w}{v}\lambda$
3. ${\lambda }^{\prime }=\frac{v_w+v}{v}\lambda$
4. ${\lambda }^{\prime }=\frac{v}{v-v_w}\lambda$

Q. When source and detector are stationary but the wind is blowing at speed , the apparent wavelength ${\lambda }^{\prime }$ on the wind side is related to actual wavelength $\lambda$ by [take speed of sound in air as v]

1. ${\lambda }^{\prime }=\lambda$
2. ${\lambda }^{\prime }=\frac{v_w}{v}\lambda$
3. ${\lambda }^{\prime }=\frac{v_w+v}{v}\lambda$
4. ${\lambda }^{\prime }=\frac{v}{v-v_w}\lambda$