Q1Multiple choice
Note is a sound
- (a)of mixture of several frequencies
- (b)of mixture of two frequencies only
- (c)of a single frequency
- (d)always unpleasant to listen
Show answer
(a) of mixture of several frequencies
(c) of a single frequency
Chapter 12
Class 9 Science · 20 questions · 18 with answers
Questions
Q2Multiple choice
A key of a mechanical piano struck gently and then struck again but much harder this time. In the second case
- (a)sound will be louder but pitch will not be different
- (b)sound will be louder and pitch will also be higher
- (c)sound will be louder but pitch will be lower
- (d)both loudness and pitch will remain unaffected
Show answer
(a) sound will be louder but pitch will not be different
Q3Multiple choice
In SONAR, we use
- (a)ultrasonic waves
- (b)infrasonic waves
- (c)radio waves
- (d)audible sound waves
Show answer
(a) ultrasonic waves
Q4Multiple choice
Sound travels in air if
- (a)particles of medium travel from one place to another
- (b)there is no moisture in the atmosphere
- (c)disturbance moves
- (d)both particles as well as disturbance travel from one place to another.
Show answer
(c) disturbance moves
Q5Multiple choice
When we change feeble sound to loud sound we increase its
- (a)frequency
- (b)amplitude
- (c)velocity
- (d)wavelength
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(b) amplitude
Q6Multiple choice
In the curve (Fig.12.1) half the wavelength is
This question refers to a figure in the original PDF.
- (a)A B
- (b)B D
- (c)D E
- (d)A E Fig. 12.1 16-04-2018
Show answer
(b) B D
Q7Multiple choice
Earthquake produces which kind of sound before the main shock wave begins
- (a)ultrasound
- (b)infrasound
- (c)audible sound
- (d)none of the above
Show answer
(b) infrasound
Q8Multiple choice
Infrasound can be heard by
- (a)dog
- (b)bat
- (c)rhinoceros
- (d)human beings
Show answer
(c) rhinoceros
Q9Multiple choice
Before playing the orchestra in a musical concert, a sitarist tries to adjust the tension and pluck the string suitably. By doing so, he is adjusting
- (a)intensity of sound only
- (b)amplitude of sound only
- (c)frequency of the sitar string with the frequency of other musical instruments
- (d)loudness of sound
Show answer
(c) frequency of the sitar string with the frequency of other musical instruments
Q10Short answer
The given graph (Fig.12.2) shows the displacement versus time relation for a disturbance travelling with velocity of 1500 m s–1. Calculate the wavelength of the disturbance. Fig. 12.2
This question refers to a figure in the original PDF.
Show answer
From the graph Time period, T = 2 × 10-6 s. Frequency, ν = 1/T = 5 × 105 Hz. Wavelength, λ = v/ν = 5 × 105 m.
Q11Multiple choice
Which of the above two graphs
This question refers to a figure in the original PDF.
- (a)and
- (b)(Fig.12.3) representing the human voice is likely to be the male voice? Give reason for your answer. Fig. 12.3 16-04-2018
Show answer
(a) and
Q12Short answer
A girl is sitting in the middle of a park of dimension 12 m × 12 m. On the left side of it there is a building adjoining the park and on right side of the park, there is a road adjoining the park. A sound is produced on the road by a cracker. Is it possible for the girl to hear the echo of this sound? Explain your answer.
Show answer
If the time gap between the original sound and reflected sound received by the listener is around 0.1 s, only then the echo can be heard. The minimum distance travelled by the reflected sound wave for the distinctly listening the echo = velocity of sound × time interval ; 344 × 0.1 ; 34.4 m But in this case the distance travelled by the sound reflected from the building and then reaching to the girl will be (6 + 6) = 12 m, which is much smaller than the required distance. Therefore, no echo can be heard.
Q13Short answer
Why do we hear the sound produced by the humming bees while the sound of vibrations of pendulum is not heard?
Show answer
Humming bees produce sound by vibrating their wings which is in the audible range. In case of pendulum the frequency is below 20 Hz which does not come in the audible range.
Q14Short answer
If any explosion takes place at the bottom of a lake, what type of shock waves in water will take place?
Show answer
Longitudinal waves.
Q15Short answer
Sound produced by a thunderstorm is heard 10 s after the lightning is seen. Calculate the approximate distance of the thunder cloud. (Given speed of sound = 340 m s–1.)
Show answer
s ; 340 m s-1 × 10 s = 3400 m or 3.4 km.
Q16Short answer
For hearing the loudest ticking sound heard by the ear, find the angle x in the Fig.12.4. Fig. 12.4
This question refers to a figure in the original PDF.
Show answer
∠i = ∠r, so x = 90° – ∠r = 90°– 50° = 40°
Q17Short answer
Why is the ceiling and wall behind the stage of good conference halls or concert halls made curved?
Show answer
Ceiling and walls are made curved so that sound after reflection reaches the target audience. Long Answer Questions
Q18Multiple choice
Represent graphically by two separate diagrams in each case
- (i)Two sound waves having the same amplitude but different frequencies?
- (ii)Two sound waves having the same frequency but different amplitudes.
- (iii)Two sound waves having different amplitudes and also different wavelengths.
Q19Multiple choice
Establish the relationship between speed of sound, its wavelength and frequency. If velocity of sound in air is 340 m s–1, calculate
- (i)wavelength when frequency is 256 Hz.
- (ii)frequency when wavelength is 0.85 m.
Show answer
(i) wavelength when frequency is 256 Hz.
Q20Long answer
Draw a curve showing density or pressure variations with respect to distance for a disturbance produced by sound. Mark the position of compression and rarefaction on this curve. Also define wavelengths and time period using this curve. SOUND 73 16-04-2018