Question 11 Mark
What does’ it mean if we say that a tuning fork has a frequency of 256 Hz?
Answer
View full question & answer→If a tuning fork has a frequency 256 Hz, then it means that it vibrates 256 times in 1 second.
Questions
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19 questions · timed · auto-graded
Question 21 Mark
Describe elasticity of a medium.
Answer
View full question & answer→Elasticity is the property of a medium to regain its shape after being stretched or compressed.
Question 31 Mark
Why do echoes produced in an empty auditorium usually decrease when it is full of people ?
Answer
View full question & answer→People absorb the sound waves travelling in the air and reduce reverberations. Whereas, in an empty auditorium, all sound waves get reflected by the walls of the autitorium.
Question 41 Mark
Why are the walls and floors of cinema halls and auditoriums covered with curtains and carpets?
Answer
View full question & answer→The walls, ceilings and floors of auditoriums and cinema halls are-covered with sound-absorbing materials such as thick sound-proofing tiles, curtains and carpets. These materials help reduce reverberations.
Question 51 Mark
What is the time period of a particle that is vibrating at a frequency of 10 Hz?
Answer
View full question & answer→Frequency, $f =10 Hz$
So, 10 vibrations are completed in $1 s$.
Therefore, time period of the sound wave $=\frac{1}{10} s =0.01 s$
So, 10 vibrations are completed in $1 s$.
Therefore, time period of the sound wave $=\frac{1}{10} s =0.01 s$
Question 61 Mark
What do you understand by the term wave?
Answer
View full question & answer→A wave is a disturbance produced in a medium that carries energy from one part of the medium to another part of the medium, without the transfer of matter.
Question 71 Mark
The frequency of a source of sound is 100 Hz. How many times does it vibrate in a minute?
Answer
View full question & answer→Frequency = 100 Hz
So, number of vibrations completed by the sound in 1 second = 100
Number of vibrations completed by it in 1 minute = 60 x 100 = 6000
So, number of vibrations completed by the sound in 1 second = 100
Number of vibrations completed by it in 1 minute = 60 x 100 = 6000
Question 81 Mark
Explain in brief about some sources of sound.
Answer
View full question & answer→Every vibrating body around us is a source of sound. A school bell, an alarm clock, a barking dog, moving vehicles and human voice are some sources of sound.
Question 91 Mark
Which type of wave motion is represented in this figure?
Answer
View full question & answer→Longitudinal wave motion is represented in the given figure.
Question 101 Mark
Identify the regions A and B.
Answer
View full question & answer→Region A shows compression while Region B shows rarefaction.
Question 111 Mark
Write some other factors on which the loudness of a sound depends.
Answer
View full question & answer→Some other factors on which the loudness of a sound depends are the atmospheric temperature, pressure, velocity of the wind and the amount of moisture present in the air.
Question 121 Mark
Name the factor based on which you drew the above conclusion.
Answer
View full question & answer→The factor on which we drew the above conclusion is the amplitude. Loudness of a sound depends on its amplitude. Higher the amplitude, louder is the sound.
Question 131 Mark
In which case the loudness of the sound is greater and why?
Answer
View full question & answer→The sound wave shown in Figure 1 is louder as it has higher amplitude.
Question 141 Mark
A girl claps and hears the echo after reflection from a cliff which is 660 m away from her. If the velocity of sound is 330 m/s, calculate the time taken for hearing the echo.
Answer
View full question & answer→Distance travelled by sound $=660 \times 2=1320 m$
Speed of sound $=330 m / s$
Speed $=\frac{\text { Distance }}{\text { Time }}=\frac{1320}{330}=2$ seconds
Speed of sound $=330 m / s$
Speed $=\frac{\text { Distance }}{\text { Time }}=\frac{1320}{330}=2$ seconds
Question 151 Mark
A boy fires a gun and hears the echo 2 seconds later. If he is 350 m away from a wall, calculate the velocity of sound in air.
Answer
View full question & answer→Distance travelled by sound $=350 \times 2=700 m$.
Time taken $=2 s$
$\text { Speed }=\frac{\text { Distance }}{\text { Time }}=\frac{700}{2}=350 m / s$
Time taken $=2 s$
$\text { Speed }=\frac{\text { Distance }}{\text { Time }}=\frac{700}{2}=350 m / s$
Question 161 Mark
What is the frequency of a wave whose time period is 0. 015 seconds ?
Answer
View full question & answer→Time period $=0.015$ seconds
Frequency = ?
We know that,
Frequency$=\frac{1}{\text { Time period }}$
$=66.66 Hz$
Frequency = ?
We know that,
Frequency$=\frac{1}{\text { Time period }}$
$=66.66 Hz$
Question 171 Mark
What is the time period of a wave with a frequency of $250\ Hz?$
Answer
View full question & answer→Given, Frequency $=250 Hz$
$T =\frac{1}{f}$
$=\frac{1}{250}$
$=0.004$ second
$T =\frac{1}{f}$
$=\frac{1}{250}$
$=0.004$ second
Question 181 Mark
Why sound travels faster on a hot summer day than on a cold winter day?
Answer
View full question & answer→As speed of the sound is directly proportional to the temperature of the medium through which it propagates, therefore sound travels faster on a hot summer day than on a cold winter day.
Question 191 Mark
Why cannot two friends talk to each other if they are on the moon?
Answer
View full question & answer→Sound requires a medium for propagation. As there is vacuum on the moon, two friends cannot hear each other there.