Chapter 7 : Sound - Range of Hearing - Frank Solutions for Class 9 Physics ICSE

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Chapter 7 - Sound - Range of Hearing Excercise 284

Question 1
What do you mean by the frequency of sound?
Solution 1
The frequency of sound is defined as the number of vibrations produced by the sound producing object per second.
Question 2
What is the SI unit of frequency?
Solution 2
S.I unit of frequency is hertz.
Question 3
Define one hertz.
Solution 3
One hertz is defined as one vibration produced in one second by sound producing object.
Question 4
What is the audible range of frequency?
Solution 4
The audible range of frequency is 20Hz to 20KHz.
Question 5
Can we hear sounds of frequencies?
(i) Less than 20 Hz?
(ii) More than 20 KHZ?
Solution 5
(i) Less than 20Hz - we cannot hear sound.
(ii) More than 20KHz - we cannot hear sound.
Question 6
Does audible range of frequency vary from person and also with the age of the person?
Solution 6
No, the audible range of frequency does not vary from person to person and also with age of person.
Question 7
What are infrasonic and ultrasonic sounds?
Solution 7
Sound having frequency less than 20Hz is called infrasonic sound.  Sound having frequency greater than 20KHz is called ultrasonic sound.
Question 8
Is the energy carried by the ultrasound very high or very low?
Solution 8
The energy carried by ultrasonic sound is very high.
Question 9
State two applications of ultrasound.
Solution 9
Applications of Ultrasonic sound
(i) Ultrasonic sound is used to detect the flaws in metal castings of automobile tyres.
(ii) It is used in hospitals to detect defects in certain parts of body.
Question 10
What is echocardiography?
Solution 10
Echocardiography is used to obtain the image of the heart by the used of ultrasonic waves.
Question 11
What does SONAR stand for? Where do we make use of SONAR?
Solution 11
SONAR stands for Sound Navigation and Ranging. Sonar helps the oceanographers and ship captains to determine the depth of the ocean.
Question 12
How are bats able to avoid obstacles in their way?
Solution 12
Bats emit the high frequencies that range between 20 KHz to 75 KHz. The echoes from these sounds help in locating the obstacles in their path and to avoid them.
Question 13
What type of sound is produced by elephants and whales?
Solution 13
The elephants and whales produce the sound of frequency less than 20Hz. (means infrasonic sounds)
Question 14
Do all animals have same ranges of audible frequencies?
Solution 14
No, all animals does not have same range of audible frequencies.
Question 15
What do you mean by an echo?
Solution 15
When the sound strike any object and reflect back, the hearing of reflected sound is called echo.
Question 16
What is echolocation? How do animals make use of this phenomenon?
Solution 16
Echolocation is defined as sending out sounds to judge the location, size and motion of objects from the returning echoes. The animals use this phenomenon to locate the obstacles in their path and avoid them so it helps them in navigation and to locate their prey.
Question 17
State three important uses of echolocation.
Solution 17
Three Important uses of echolocation:::
(i) It helps animals to communicate with each other. e.g dolphins use the echolocation to communicate with other dolphins.
(ii) It helps in navigation and to locate their prey.
(iii) It is used by them to hunt for the meal.
Question 18
What are hearing aids?
Solution 18
A hearing aid is the device which increases the loudness and intensity of the incoming sound.
Question 19
State the main components of a hearing aid.
Solution 19
The main components of hearing aid are microphone , amplifier and  earphone.
Question 20
Describe a simple method to find the depth of a submerged ship.
Solution 20
A ship sends ultrasonic waves downward in the ocean. When the sound waves reaches the ocean floor , they are reflected back to the ship . The time it takes for the signal to return is used to calculate the depth of submerged ship in the ocean.
Question 21
State the properties of ultrasound that make it useful.
Solution 21
High Power , High Energy and good directionality are the properties of ultrasonic sounds which makes them useful.
Question 22
Name the sounds of the frequencies given below:
(i) 10 Hz
(ii) 200 Hz
(iii) 2000 Hz
(iv) 45 kHz
Solution 22
(i) 10 Hz - Infrasonic sound.
(ii) 200Hz - audible sound.
(iii) 2000 Hz - Audible sound.
(iv) 45 KHz - Ultrasonic sound