## Samacheer Kalvi 9th Term III Science Book Back Question and Answers – Unit 2:

Samacheer Kalvi 9th Standard New Science Book Back 1 Mark and 2 Mark Question & Answers PDF uploaded and available below. Class 9 New Syllabus 2021 to 2022 Book Back Question & Answer solutions available for both English and Tamil Medium. Class 9 Science Book Term 3 Unit 2 – Sound Answers/Solutions are provided on this page. 9th Std Science Book is of Term 1st, 2nd, 3rd, and consists of 9 Units in each Term. All 9 Units of Term 1st, 2nd, 3rd Science Book Back One, and Two Mark Solutions are given below.

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### Samacheer Kalvi 9th Science Book Back Term 3 Unit 2 Solutions Guide PDF:

Science Subject 1 Mark and 2 Mark Solutions Guide PDF available below. Click the Download option to download the book back 1 Mark & 2 Mark questions and answers. Take the printout and use it for exam purposes.

### I. Choose the correct answer:

1. Which of the following vibrates when a musical note is produced by the cymbals is an orchestra?
a) stretched strings  b) stretched membranes
c) air columns           d) metal plates

2. Sound travels in the air:
a) if there is no moisture in the atmosphere
b) if particles of medium travel from one place to another.
c) if both particles as well as disturbance move from one place to another.
d) if disturbance moves.

3. A musical instrument is producing continuous note. This note cannot be heard by a person having a normal hearing range. This note must then be passing through.
a) wax      b) vacuum
c) water   d) empty vessel

4. If the speed of a wave is 340ms4 and its frequency is 1700 Hz, then wavelength λ for this wave in cm will be
a) 34   b) 20
c) 15    d) 0.2

5. Which of the following statement best describes frequency?
a) the number of complete vibrations per second.
b) the distance travelled by a wave per second.
c) the distance between one crest of wave and the new one.
d) the maximum disturbance caused by a wave.

6. The maximum speed of vibration which produces audible sound will be in
a) sea water   b) ground glass
c) dry air        d) human body

7. The sound waves travel faster
a) in liquids       b) in gases
c) in solids     d) in vacuum

8. When the pitch of note by a harmonium is lowered, then the wave length of the note
a) first decreased and then increases   b) decreases
c) remains the same                                 d) increases

9. The speeds of sound in four different media are given below which of the following is the most likely speed in ms-1 with which the two under water whales in a sea can talk to each other when separated by a large distance.
a) 5170   b) 1280
c) 340       d) 1530

10. Which of the following can produce longitudinal waves as well as transverse waves under different conditions?
a) TV transmitter   b) tuning fork

11. The velocities of sound waves in four media P,Q,R and S are 18000 km/h, 900 km/h, 0 km/h and 1200 km/h respectively. Which could be a liquid medium?
a) R     b) Q
c) P     d) S

### II. Fill in the blanks:

1. Vibration of objects produces sound.
2. Sound is a mechanical wave and needs a material medium to travel.
3. Number of vibrations produced in one second is frequency.
4. The velocity of sound in solid is greater than the velocity of sound in air.
5. Loudness in proportional to the square of the amplitude.
6. A sound wave has a frequency of 4 k Hz and wave length 2 m. Then the velocity of sound is 8000m.s-1
7. Stethoscope is a medical instrument used for listening to sounds produced in the body.
8. The repeated reflection that results in persistence of sound is called reverberation.
9. Ultrasounds can also be used to detect cracks and flaws in metal blocks.
10. In the inner ear, the pressure variations are turned into electrical signals by the cochlea.

### III. Match the following:

1. Tuning fork     a) The point where the density of air is maximum.
2. Sound               b) Maximum displacement from the equilibrium position.
3. Compressions c) The sound whose frequency is greater than 20,000 Hz.
4. Amplitude       d) Longitudinal wave
5. Ultrasonics      e) production of sound
Ans: 1-e ; 2-d ; 3-a ; 4-b ; 5-c.

IV. Matrix matching:

 1. Loudness a. Number of vibrations produced in unit time A. Decibel 2. Time period b. The amount of sound produced/ received B. Metre 3. Amplitude c. Distance travelled by sound in unit time C. Hertz 4. Velocity of sound d. The time required to produce one complete wave D. Metre per second 5. Frequency e. The maximum displacement from the mean position E. Second

Ans: 1 –b-A; 2- d- E; 3- e – B; 4- c- D; 5 –a- C

### V. Short Questions & Answers:

1. Name the device which is used to produce sound in laboratory experiments.
A tuning fork is used to produce sound in laboratory experiments.

2. Through which medium does sound travel faster, iron or water? Give reason.
Sound travels faster in iron medium. One of the conditions for the velocity of sound is density. The density of iron is greater than the density of water. So sound travels faster in iron.

3. What should an object do to produce sound?
To produce sound, the object should vibrate.

4. Can sound travel through vacuum?
No, sound cannot travel through vacuum.

5. Name the physical quantity whose SI unit is ‘hertz’ Define.
The SI unit of frequency is hertz (Hz). A complete cycle produced in one second is called hertz.

6. What is meant by supersonic speed?
When the speed of any object exceeds the speed of sound in air (330 ms-1), it is said to be supersonic speed.

7. How does the sound produced by a vibrating object in a medium reach your cars?
When an object vibrates, it sets the particles of the medium around to vibrate. But, the vibrating particles do not travel. A particle of the medium in contact with the vibrating object is displaced from its equilibrium position. It then exerts a force on an adjacent particle which gets displaced from its position of rest. After that the first particle comes back to its original position. This process continues in the medium till the sound reached our ears.

8. You and your friend are on the moon. Will you be able to hear any sound produced by your friend?
No. As there is no medium like air on the moon, the sound waves do not travel.