NCERT Exemplar Solution Class 9 Science Chapter 12
NCERT Exemplar Solution Class 9 Science Chapter 12 Sound all Questions Answer Solution. NCERT Exemplar Class 9 Science Chapter 12 Solution PDF.
NCERT Exemplar Solution Class 9 Science Chapter 12: Overview
NCERT Exemplar Solution Class 9 Science Chapter 12 |
|
Board |
NCERT |
Topic |
Exemplar Problem Solution |
Class |
9 |
Subject |
Science |
Chapter |
12 |
Chapter Name |
Sound |
NCERT Exemplar Solution Class 9 Science Chapter 12 Sound
Multiple Choice Questions
1) 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
Answer:- a) of mixture of several frequencies.
Explanation: Vibration produces frequency , these different types of frequency produces sound.
2) 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
Answer:- a) sound will be louder but pitch will not be different.
Explanation: At same pitch if the force is greater then the sound can be louder.
3) In SONAR, we use
a) Ultrasonic waves
b) Infrasonic waves
c) Radio waves
d) Audible sound waves
Answer:- a) Ultrasonic waves
Explanation: Ultrasonic waves are used in SONAR system.
4) 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
Answer:- c) disturbance moves.
Explanation: Sound travels in air when the vibrations propagate sound waves. And the disturbance formed by the vibration is moved from one place to another place.
5) When we change feeble sound to loud sound we Increase it’s
a) Frequency
b) Amplitude
c) Velocity
d) Wavelength
Answer:- b) amplitude
Explanation: Feeble sound Increase loud sound due to its amplitude as amplitude is directly proportional to sound’s loudness. Higher the Amplitude higher the loudness.
6) In the curve (fig. 12.1) half the wavelength is
a) AB
b) BD
c) DE
d) AE
Answer:- b) BD
Explanation: In the given curve the half wavelength is BD. Because a wavelength is the distance of the two consecutive trough or two consecutive crest. Thus a full wavelength is AE.
7) Earthquake produces which kind of sound before the main shock wave begins
a) Ultrasound
b) Infrasound
c) Audible sound
d) None of the above
Answer:- infrasound.
Explanation: Earthquake produces infrasound which is received by some animals.
8) Infrasound can be heard by
a) Dog
b) Bat
c) Rhinoceros
d) Human beings
Answer:- C) Rhinoceros
Explanation: Rhinoceros can listen the sound waves below the 20 Hz and below 20 Hz is the infrasound waves frequency.
9) Before playing the orchestra in a musical concert, a sitaristtries 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
Answer:- c) Frequency of the sitar string with the frequency of other musical instruments
Explanation: By adjusting the sugar’s tension the artists tries to adjust the frequency of the sitar. And he pluck the string suitably to check whether the sitar is tuned or not.
Short Answer Questions
10) 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.
Answer:-
We have to calculate the wavelength of the disturbance,
So,
V (frequency) = 1/T
Here , T = 2× 10 6 Hz
Therefore,
V= 1 / 2×106
V= 10 5 Hz
Now, for calculating the wavelength
We have
Wavelength =v / V = 5 × 105 m
Thus the wavelength is 5 × 10 5 m.
11) Which of the above two graphs (a) and (b) (fig. 12.3) representing the human voice is likely to be the male voice? Give reason for your answer.
Answer:- here in the given graphs the male voice is represented by the graph a. Because male voice has lighter pitch and less wavelengths than the female voice.
12) 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.
Answer:-
No. The echo will not be it heard by the girl in these situation, because when the sound travels within 0.1 s gap then only echo can he listened.
= Velocity of sound × time interval
= 344 × 0.1
= 34.4 m
So the distance if the sound should be bear about 34.4 m but in these case the distance of the sound is 12 m which is smaller than the distance so the echo will not be listened.
13) Why do we hear the sound produced by the humming bees while the sound of vibrations of pendulum is not heard?
Answer:-
Human beings can hear the sound between the frequency of 20 Hz to 20000 Hz which is also known as audible frequency. The humming Bird produces the sound between these range thus we can hear the sound. But pendulum does not produce the sound between the audible range thus we cannot listen to the sound of pendulum.
14) If any explosion takes place at the bottom of a lake, what type of shock waves in water will take place?
Answer:-
If the explosion takes place at the bottom of the lake then longitudinal waves will take place in the water.
15) Sound produced by a thunderstorm is heard 10 s after the Lightning is seen. Calculate the appropriate distance of the thunder cloud. ( Given speed of sound= 340 m s-1)
Answer:-
Given –
Speed of sound = 340 m s-1
Time = 10 s
Distance =?
Now,
Distance = speed × time
Distance = 340 × 10
Distance = 3400 m .
Thus the distance of the thunder cloud is 3400 m.
16) For hearing the loudest ticking sound heard by the ear, find the angle x in the fig. 12.4 .
Answer:-
We have to find the angle x which is the angle of reflection.
Angle of incidence = angle of reflection
Angle of incidence = 90° – 50°
Angle of incidence = 40°
Therefore, angle of reflection = 40°.
Thus, x = 40°
17) Why is the ceiling and wall behind the stage of food conference halls or concert halls made curved?
Answer:-
The curved given to the walls and ceiling reflect the sound maximum to reach to the people and sound should be listened well.
Long Answer Questions
18) Represent graphically by two separate diagrams in each case
I) Two sound waves having the same amplitude but different frequencies?
Answer :-
Same frequency but different amplitude
ii) Two sound waves having the same frequency but different Amplitudes
Same frequency but different amplitude
iii) Two sound waves having different Amplitudes and also different wavelengths.
Answer:-
Different amplitudes and different wavelengths
19) Establish the relationship between speed of sound, it’s wavelength and frequency. If velocity of sound in air is 340 m s-1, Calculate
i) Wavelength when frequency is 256 Hz.
Answer:-
Wavelength = ?
Velocity = 340 Hz
Frequency = 256 Hz.
Velocity = frequency × wavelength
340 = 256 × wavelength
Wavelength = 340/256
Thus, wavelength = 1.33 m.
ii) frequency when wavelength is 0.85 m.
Answer:-
Wavelength = 0.85 m
So,
Velocity= frequency × wavelength
340 = frequency × 0.85
340/0.85 = frequency
Thus, V= 400 Hz
Frequency is 400 Hz.
20) 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.
Answer:-
Wavelength →
The distance between the two consecutive crest or two consecutive through is the wavelength.
Time period →
The time taken to travel by one wavelength is known as time period.