WBCHSE Class 11 Physics Doppler Effect In Sound and Light Multiple Choice Questions

by

Doppler Effect In Sound  and Light Multiple Choice Questions

Question 1. A source of sound with a frequency of 256 Hz is moving with a velocity of v towards a wall and an observer is stationary between the source and the wall. When the observer is between the source and the wall

  1. He will hear beats
  2. He will hear no beats
  3. He will not get any sound
  4. He will get the sound of the same frequency

Answer: 2. He will hear no beats

Question 2. The frequency of a progressive wave may change due to

  1. Reflection
  2. Refraction
  3. Interference
  4. Doppler effect

Answer: 4. Doppler effect

Question 3. A train blowing a whistle of frequency 1000 Hz is moving with a uniform velocity from west to east. The apparent frequency of the sound of the whistle to a stationary listener is 990 Hz. The position of the listener relative to the train is

  1. On the north
  2. On the south
  3. On the east
  4. On the west

Answer: 4. On the west

Question 4. A source of sound and a listener are moving in the same direction with the same velocity. If the actual frequency of sound is 200 Hz, the apparent frequency of the sound to the listener is

  1. 200 Hz
  2. Less than 200 Hz
  3. Greater than 200 Hz
  4. None of these

Answer: 1. 200 Hz

Question 5. A bus is moving towards a huge wall with a velocity of 5 m · s-1. The driver sounds a horn of frequency 200 Hz. The beat frequency heard by the passenger will be

  1. 4
  2. 6
  3. 8
  4. 2

Answer: 2. 6

WBCHSE Class 11 Physics Doppler Effect In Sound and Light Multiple-Choice Questions

Question 6. A motor car sounding a horn is approaching a large reflector. If the frequency of the horn is 1000 Hz, the frequency of the echo to the driver will be

  1. 1000 Hz
  2. Less than 1000 Hz
  3. Greater than 1000 Hz
  4. None of these

Answer: 3. Greater than 1000 Hz

Question 7. An observer standing on a railway crossing receives frequencies of 2.2 kHz and 1.8 kHz when the train approaches and recedes from the observer. The speed of the sound in air is 300 m · s-1. The velocity of the train (in m · s-1)

  1. 60
  2. 30
  3. 90
  4. 70

Answer: 2. 30

Question 8. A whistle producing sound waves of frequency 9500 Hz and above is approaching a stationary person with speed v m · s-1. The velocity of sound in air is 300 m · s-1. If the person can hear frequencies upto a maximum of 10000 Hz, the maximum value of v up to which he can hear the whistle is

  1. 15√2 m · s-1
  2. 15/√2 m · s-1
  3. 15 m · s-1
  4. 30 m · s-1

Answer: 3. 15 m-s-1

Question 9. What do you understand by the red shift of a star or of a galaxy of stars?

  1. They are gradually receding from the earth
  2. They are gradually approaching the earth
  3. They are stationary
  4. None of the above

Answer: 1. They are gradually receding from the earth

Question 10. When a source of light and an observer approach each other, the apparent change of the wavelength of light is called

  1. Redshift
  2. Violet shift
  3. Blueshift
  4. Black shift

Answer: 3. Blueshift

In this type of questions, more than one options are correct.

Question 11. State in which of the following cases, an observer will not see any Doppler effect?

  1. Both the source and observer remain stationary but a wind blows.
  2. The observer remains stationary but the source moves in the same direction and with the same speed as the wind.
  3. The source remains stationary but the observer and the wind have the same speed away from the source.
  4. The source and the observer move directly against the wind but both with the same speed.

Answer:

1. Both the source and observer remain stationary but a wind blows.

4. The source and the observer move directly against the wind but both with the same speed.

Question 12. Consider a source of sound S and an observer P. The sound source is of frequency n0. The frequency observed by P is found to be n1 if P approaches S at speed v and S is stationary, n2 if S approaches P at speed v and P is stationary and n3 if each of P and S has speed \(\frac{v}{2}\) towards one another. Which of the following conclusions is correct?

  1. n1 = n2 = n3
  2. n1< n2
  3. n3 > n0
  4. n3 lies between n1 and n2

Answer:

2. n1< n2

3. n3>n0

4. n3 lies between n1 and n2

Question 13. An observer A is moving directly towards a stationary sound source while another observer B is moving away from the source with the same velocity. Which of the following conclusions are correct?

  1. The average of frequencies recorded by A and B is equal to the natural frequency of the source.
  2. The wavelength of waves received by A is less than that of waves received by B.
  3. The wavelength of waves received by two observers will be the same.
  4. Both observers will observe the wave travelling at same speed.

Answer:

1. The average of frequencies recorded by A and B is equal to natural frequency of the source.

3. The wavelength of waves received by two observers will be the same.

Question 14. Two cars, each moving with speed u on the same horizontal straight road, are approaching each other. Wind blows along the road with velocity w. One of these cars blows a whistle of frequency f1. An observer in the other car hears the frequency of the whistle to be f2. The speed of sound in still air is v. Correct statement(s) is are:

  1. If the wind blows from the observer to the source, f2 > f1
  2. If the wind blows from the source to observer, f2>f1
  3. If the wind blows from the observer to the source, f2<f1
  4. If the wind blows from the source to the observer, f2<f1

Answer:

  1. If the wind blows from the observer to the source, f2 > f1
  2. If the wind blows from the source to the observer, f2>f1
  3. If the wind blows from the observer to the source, f2<f1

Leave a Comment