# CBSE Class 11-science Physics Doppler Effect

- Answer ques 1
- Plz answer 12th sum
- The apparent frequency of the whistle of an engine changes in the ratio 3 : 2 as the engine passes a stationary observer. If the velocity of sound is 330 m/s, calculate the velocity of the engine.
- What is Doppler's effect in sound waves? Give an example. What is the cause of Doppler's effect?
- If n
^{'}is the apparent frequency, n is the true frequency, u_{s }is the velocity of source, u_{0}is the velocity of observer and V is the velocity of sound, then write the following results : (i) Observer at rest, source in motion towards the observer. (ii) Observer at rest, source in motion away from the observer. (iii) Source at rest, observer source in motion towards the source. (iv) Source at rest, observer in motion away from the source. (v) Source and observer both moving away from each other. (vi) Source and observer both moving towards each other. (vii) Source and observer both in motion in the same direction with the same velocity. - Obtain an expression for the apparent frequency of a note heard by an observer when, (a) source alone is in motion towards the observer. (b) source alone is in motion away from the observer. (c) observer alone is in motion towards the observer. (d) observer alone is in motion away from the observer. (e) when the source and observer are moving towards each other.
- How does the apparent frequency change when there is relative motion between the source of sound and observer?
- Name some applications of Doppler's effect.
- The whistle of an approaching engine appears to be shriller than that of a receding engine. Why?
- A source of sound produces waves of wavelength 28 cm. The source is moving with velocity 12 m/s due east. Find the apparent wavelength of wave received by observer on (i) east (ii) west of source. Take velocity of sound in air 336 m/s.

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