Science Chapter 18 Flashcards
1
Q
Bats detect the obstacles in their path by receiving the reflected ………….. .
A
Ultra sonic waves
2
Q
An object that moves back and forth is called ……………. .
A
An oscillator
3
Q
If the length of a pendulum is increased the time period of oscillation ………………. .
A
Increases
4
Q
The …………… of a wave is the maximum distance moved by the object on either side of the mean position.
A
Amplitude
5
Q
Sound waves do not travel through ……………… .
A
Vaccum
6
Q
The frequency above which sound is not audible to the human ear is …………….. .
A
50,000 Hz
7
Q
Number of vibrations in a second is called …………….. .
A
Frequency
8
Q
Higher the frequency greater will be the ………….. .
A
Pitch
9
Q
The loudness of sound depends on ………….. .
A
Amplitude
10
Q
Loudness of sound is measured in units of ………………. .
A
Decibel dB
11
Q
100 hertz is equal to hundred oscillations in ………………. .
A
One second
12
Q
The sound frequencies above 20,000 Hz.
A
Ultra sonic sound
13
Q
The medium through which sound is most clearly propagated.
A
Solids
14
Q
The range of frequency in which humans can hear sound.
A
20 - 20,000Hz
15
Q
The sound level physically painful to humans.
A
Above 100 dB
16
Q
The technique used by bats to find their way.
A
echolocation
17
Q
The unit of frequency of sound.
A
Hertz
18
Q
The scientist in whose honour was the unit decibel named for intensity of sound.
A
Alexander graham Bell
19
Q
Bats and dolphins can hear these sound frequencies.
A
Ultra sonic sound
20
Q
The sound frequencies used in RADAR systems.
A
Ultra sonic sound
21
Q
The unit of sound level or intensity.
A
Decibel (dB)
22
Q
How is sound produced?
A
Sound is produced by vibration of an object.
23
Q
What produces sound in human beings ?
A
The vibration of the vocal chords in our larynx or voice box produces sound.
24
Q
What is oscillatory motion?
A
To and fro motion of an object (oscillator) on either side of a central position is called oscillatory motion.
25
What is periodic motion?
The motion of an object repeated again and again at fixed intervals of time is called periodic motion.
26
What is frequency of oscillation?
The number of oscillations completed by an oscillator in one second is called the frequency of oscillation.
27
How is intensity of sound and amplitude of vibration related?
The intensity of sound is proportional to the square of the amplitude of vibration. For example, if the amplitude is doubled the intensity becomes four times as much.
28
What happens if the frequency of sound is greater than 1000 Hz or 100 dB?
If frequency of sound is increased more than 100dB, the hearing can be temporarily affected which can result in temporary deafness.
29
What is infrasonic sound
A sound with a frequency less than 20Hz is called infrasonic sound.
30
What is application of ultrasonic sound?
Ultrasonic sound is used in ships as a system known as ‘SONAR’ to detect the obstacle beneath the ocean as well as the depth of an ocean.
31
What is the difference between pitch and frequency?
Pitch is directly proportional to the frequency of a sound whereas frequency is the repeating vibrations per unit time.
32
What happens when the rubber band is stretched with a greater force and released?
When a rubber is stretched with a greater force and released, the amplitude increases which in turn result in a louder sound being generated.
33
What happens to frequency if the amplitude is changed?
The frequency remains the same even if the amplitude is increased or decreased.
34
Define :- Echo
It is a repetition of sound due to the reflection of original sound by a large and hard obstacle.
35
Define:-Frequency
It is defined as the number of vibrations per unit time.
36
Define :- Hertz
One hertz is one vibration per second.
37
Define :- Ultra sonic vibrations
Sounds of frequency higher than 20,000 Hz are called the ultrasonic.
38
Define :- Time period
The time taken by an object to complete one oscillation is called time period.
39
Define :- Amplitude
The distance between the mean or central position to the extreme position of an oscillator on either side is called amplitude.
40
Say True or False with explanation:
Sound cannot travel in vacuum.
True. Sound needs a medium to travel through. Since vacuum does not provide any medium, sound cannot travel through it.
41
Say True or False with explanation:
If the amplitude of vibration is large, sound is feeble.
False. When the amplitude of vibration of a sound is large, the sound is very loud. The sound is feeble, when the amplitude is small. Loudness of a sound is proportional to the square of the amplitude of its vibration.
42
Say True or False with explanation:
For human ears, the audible range is 2 Hz to 20,000 Hz.
True. Human being can hear sounds only within the range of 20-20,000 Hz. We cannot hear the sound having frequency out of this range.
43
Say True or False with explanation:
The lower the frequency of vibrations the higher is the pitch.
False. Pitch of sound increases when the frequency of vibration increases. The pitch of a sound is directly proportional to its frequency.
44
Say True or False with explanation:
Unwanted or unpleasant sound is termed as music.
False. Unwanted, or unpleasant sounds are termed noise. Sounds which are melodious, and pleasing to ears are called music.
45
Say True or False with explanation:
Noise pollution may cause partial hearing impairment.
True. Unwanted, unpleasant sounds are called noise. If one is subjected to noise continuously for a long time, one may suffer from partial hearing impairment.
46
Say True or False with explanation:
Time taken by an object to complete one oscillation is called time period.
True. Time taken by an object to complete one oscillation is called time period.
47
A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.
Frequency is the number of oscillations per second of a vibrating body.
Number of
Oscillation
Frequency = ----------------------
Total time
taken
The time taken to complete one oscillation (to and fro) is known, as time period.
1
Time period = ---------------------
Frequency of
oscillation
1
= --------------- = 0.1 seconds
10
48
The sound from a mosquito, is produced when it vibrates its wings at an average rate of 500 vibrations per second. What is the time period of the vibration?
The time taken to complete one oscillation (to and fro) is know as time period.
1
Time period = --------------------
Frequency of
oscillation
49
50
Why should loud speakers should not be put in congested areas?
The loudness or softness is indicated by the intensity of sound and sound level.
By putting loud speakers in congested areas, the intensity of sound being more than 100 dB will cause ill effects like temporary deafness and a prolonged exposure can lead to permanent damage.
51
Why are the ceilings of concert halls curved?
The ceilings of concert halls are curved because sound after reflection from the ceiling it reaches all the comers of the hall and is audible to each person in the hall.
52
Have you ever heard the sound of movement of hands and falling of leaves from a tree?
The term infrasonic refer to sound waves below the frequencies of audible sound i.e. under 20 Hz.
Humans cannot hear infrasonic sound.
Movement of hands and falling of leaves comes below this audible range. Therefore we cannot hear these sounds.
53
How can dogs perceive in advance the signals of an impending earthquake?
Dogs can hear sounds upto about 65,000 Hz. That’s why dogs can receive ultrasonic sound signals produced by the vibration of the earth and start barking in advance before the actual earthquake is felt.
54
State the uses of Ultrasonic sound.
To clean delicate ornaments and the tiny parts of a watch.
To observe internal organs of the body.
To detect tumors in the brain.
To detect faults in a metal.
In RADAR systems
To Kill certain microbes and insects.
SONAR (Sound navigation and ranging) is used to locate the seabed or the position of a ship.
55
Will a sound be generated no matter how the ruler is kept on the table.
No, If the ruler kept on the table is only a little part off the table, it will not vibrate with a greater force.
On the contrary if the ruler is kept with a larger portion off the table it will vibrate with a greater force generating louder sound.
56
Is there any correlation between the length of the free part of the ruler and the sound generated?
Yes, vibrating ruler pushes the molecules in the air producing sound waves. More the length of free part of ruler less will be the vibrations and less will be the frequency and pitch of the sound. If the length of free part of ruler is shorter it vibrates more quickly producing sound of higher frequency and pitch.
57
If the ruler is plucked while it is held with 25 cm of it off the table, does it makes any sound? If there is no sound, look for the reason why it is so?
No, the ruler vibrates very slowly, which has frequency which is not audible.
58
What would be the difference perceived between hearing only two pupils in the class talking to each other and all the children talking to one another at the same time?
When two pupils talk to each other, the sounds of two frequencies produced can be heard clearly.
When all the children talk to one another sounds of many frequencies produced can not be heard clearly.
Sound level will be more creating loud noise.
