Question 1

Question 1:
Can sound travel through (a) iron, and (b) water?

Accepted Answer

Answer:
Yes, sound can travel through iron as well as water.

Question 2

Question 2:
Can sound travel through vacuum?

Accepted Answer

Answer:
No, sound cannot travel through vacuum because sound wave requires a material medium for its propagation.

Question 3

Question 3:
Name the type of waves which are used by astronauts to communicate with one another on moon (or in outer space).

Accepted Answer

Answer:
Radio waves are used by astronauts to communicate with one another on moon because radio waves do not require any material medium for its propagation.

Question 4

Question 4:
Name one solid, on liquid and one gas through which sound can travel.

Accepted Answer

Answer:
Sound waves require a material medium for its propagation so that it can travel in all the three states of matter:
solid (iron block), liquid (water), and gas (hydrogen).

Question 5

Question 5:
Which of the following cannot transmit sound?
Water, Vacuum, Aluminium, Oxygen gas

Accepted Answer

Answer:
Among the following, vacuum cannot transmit sound because sound waves require a material medium for its propagation.

Question 6

Question 6:
Name the physical qantity whose SI unit is 'hertz'.

Accepted Answer

Answer:
Frequency is the physical quantity and its SI unit is hertz (Hz).

Question 7

Question 7:
What is the SI unit of frequency?

Accepted Answer

Answer:
The SI unit of frequency is hertz (Hz).

Question 8

Question 8:
What type of wave is represented :

(a) by density-distance graph?
(b) by displacement-distance graph?

Accepted Answer

Answer:
(a) Longitudinal waves are represented by density–distance graph.
(b) Transverse waves are represented by displacement–density graph.

Question 9

Question 9:
Is the speed of sound more in water or in steel?

Accepted Answer

Answer:
Sound travels faster in steel than in water. In solids, the distances between the molecules are closer and thus the atoms are more densely packed than in liquids. Therefore, the molecules quickly collide with one another and transfer the vibrational energy.

Question 10

Question 10:
In which medium sound travels faster : air or iron?

Accepted Answer

Answer:
Sound travels faster in iron than in air. In solids, the distances between the molecules are closer and thus the atoms are more densely packed than in gases. Therefore, the molecules quickly collide with one another and transfer the vibrational energy.

Question 11

Question 11:
In which medium sound travels fastest : air, water or steel?

Accepted Answer

Answer:
Sound travels faster in steel than in water. Similarly, sound travels faster in water than in air. This is because in solids, the distances between the molecules are closer and thus the atoms are more densely packed than in gases and liquids. Therefore, the molecules quickly collide with one another and transfer the vibrational energy. Similarly, in liquids the molecules are closer to one another than in gases.

Question 12

Question 12:
Out of solids, liquids and gases :

(a) in which medium sound travels slowest?
(b) in which medium sound travels fastest?

Accepted Answer

Answer:
In solids, the distances between the molecules are closer and thus the atoms are more densely packed than in gases and liquids. Therefore, the molecules quickly collide with one another and transfer the vibrational energy. Similarly, in liquids the molecules are closer to one another than in gases. Therefore, the following data is inferred:

(a) Sound travels slowest in gases.
(b) Sound travels fastest in solids.

Question 13

Question 13:
Which of the following is the speed of sound in copper and which in aluminium?

(a) 5100 m/s
(b) 1500 m/s
(c) 3750 m/s

Accepted Answer

Answer:
(a) Speed of sound in copper νcopper = 3,750 m/s.
(b) Speed of sound in aluminium νaluminium = 5,100 m/s.

Question 14

Question 14:
If you want to hear a train approaching from far away, why is it more convenient to put the ear to the track?

Accepted Answer

Answer:
It is more convenient to put the ear to the track to hear a train approaching from far away because sound travels faster in solids than in air because the speed of sound is directly proportional to the density of the material medium. In this case, the density of railway track is higher than air. Hence, sound waves travel faster through the railway track.

Question 15

Question 15:
What is the speed of sound :

(a) in air?
(b) in water?
(c) in iron?

Accepted Answer

Answer:
Speed of sound in
(a) air is 344 m/s,
(b) water is 1,500 m/s, and
(c) iron is 5,130 m/s.

Question 16

Question 16:
What name is given to those aircrafts which fly at speeds greater than the speed of sound?

Accepted Answer

Answer:
Supersonic aircraft are aircraft that fly at speeds greater than the speed of sound.

Question 17

Question 17:
A jet aircraft flies at a speed of 410 m/s. What is this speed known as?

Accepted Answer

Answer:
Supersonic speed, because 410 m/s is higher than the speed of sound in air (340 m/s).

Question 18

Question 18:
What is meant by supersonic speed?

Accepted Answer

Answer:
Supersonic speed is a rate of travel of an object that exceeds the speed of sound in air.

Question 19

Question 19:
State one observation from everyday life which shows that sound travels much more slow than light.

Accepted Answer

Answer:
During rainy season, it is a common observation that the flash of lightning is seen first while the sound of thunder is heard a little later. This is because light (3 × 108 m/s) travels faster than sound (340 m/s) in air.

Question 20

Question 20:
Name the two types of waves which can be generates in a long flexible spring (or slinky).

Accepted Answer

Answer:
Transverse and longitudinal waves can be generated in a long flexible spring.

Chapter 5 : Sound