Waves and Energy

 C. Short questions

1. Give at least two differences between mechanical waves and electromagnetic waves.

Ans: Difference b/w mechanical waves and electromagnetic waves. Mechanical Waves:

1. These waves required a material medium to travel.

2. These waves cannot through vacuum.

Electromagnetic waves:

1. These waves do not require a material medium to travel.

2. These waves can posses through vacuum

2. Differentiate between transverse waves and longitudinal waves. Give at least one similarity and one difference. Ans: Transverse Waves:

(1) In these waves particles of the medium vibrates perpendicular to direction of wave.

(2) These waves consist of crest and trough. Similarities:

These are mechanical cal waves. These waves cannot pass through vacuum.

Longitudinal waves:

(1) In these waves particles of the medium vibrates parallel to the direction of wave.

(2) These waves consist of compression and rarefaction. These are also mechanical waves. These waves also cannot pass through vacuum.

3. Why do we not hear sound caused by explosions on the sun?

Ans: We cannot hear sound caused by explosions on the sun because there is space b/w earth and sun and the sound waves cannot travel through space. Therefore these: sound cannot reach us due to vacuum.

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4. Define the following terms: crest, trough, rarefaction and compression 

1.Crest

It is the portion of transverse

wayes above the mean position.

2.Trough 

It is the portion of transverse

waves below the mean position.

3.Rarefaction 

The portion of longitudinal wave in which particle of medium are spread out is called rarefaction.

4.Compression:

The portion of longitudinal wave in which particles of medium are close to each other is called compression. 

7. How an a body produce sound? Explain briefly.

Ans: A body can produce sound by beating or plucking its surface. By doing so we can see that the surface of the body are vibrating on disturbing. Therefore sound is produced by vibrating bodies and travel away from vibrating body.

8. What is pitch of sound? How is it related with the frequency of sound? Ans: Pitch of sound:

It is a property of sound which tells us how shrill or grave sound is pitch of sounds helps us to distinguish between sound of different frequencies, because pitch of sound is directly related with the frequency of sound. Children, girls, birds and whittling sound are shrill and have greater frequencies. While lion's roar, man, and dog sounds. are grave and have smaller frequencies. Hence large frequency sounds have larger pitch.

9.What is loudness of sound? Name the factors on which loudness of sound depend.

Ans:Loudness of Sound: Loudness of sound is the sensation produced by sound on our ears. This property helps us to distinguish between a soft sound and a louder sound. Following are some factor which

affect loudness of sound.

(1) Amplified of the waves. 

(2) Surface Area of sound source.

(3) Distance form sound source. 

(4) Sensitivity of Ear.

10. A mobile phone is vibrating in your hand and another mobile is vibrating on a table. Which will be producing louder sound and why?

Ans:A mobile phone vibrating on a table would produce louder sound than vibrating in our hand because these vibration, produces more vibration on the surface of table. Also the surface area of the table is greater than the hand therefore mobile vibrating on table will produce louder sound.

11. How can you hear echo?

Ans: Echo:

Echo is the repetition of sound due to reflection of sound waves from a hard surface. Hence, when we speak in a big empty hall or shout towards hard wall a hill, the sound reflected back and after some time we hear echo. We can hear echo when the time gap b/w original sound and reflected it at least 0.1 sec and reflecting surface should be at least 17 meters.

12. In a cricket ground, batsman hits four in a test match. You notice that hitting sound of the bat is heard slightly after you see the bat actually hitting the ball. Why is it so?

Ans:We have noticed that hitting sound of the bat is heard slightly after we see that bat actually hitting the ball, this is due to the slow speed of sound in air. The hitting of a bat is fC. Short questions

1. Give atleast two differences between mechanical waves and electromagnetic waves.

Ans: Difference b/w mechanical waves and electromagnetic waves. Mechanical Waves:

1. These waves required a material medium to travel.

2. These waves cannot through vacuum.

Electromagnetic waves:

1. These waves do not require a material medium to travel.

2. These waves can posses through vacuum

2. Differentiate between transverse waves and longitudinal waves. Give at least one similarity and one difference. Ans: Transverse Waves:

(1) In these waves particles of the medium vibrates perpendicular to direction of wave.

(2) These waves consist of crest and trough. Similarities:

These are mechanical cal waves. These waves cannot pass through vacuum.

Longitudinal waves:

(1) In these waves particles of the medium vibrates parallel to the direction of wave.

(2) These waves consist of compression and rarefaction. These are also mechanical waves. These waves also cannot pass through vacuum.

3. Why do we not hear sound caused by explosions on the sun?

Ans: We cannot hear sound caused by explosions on the sun because there is space b/w earth and sun and the sound waves cannot travel through space. Therefore these: sound cannot reach us due to vacuum.

4. Define the following terms: crest, trough, rarefaction and compression 

1.Crest

It is the portion of transverse

wayes above the mean position.

2.Trough 

It is the portion of transverse

waves below the mean position.

3.Rarefaction 

The portion of longitudinal wave in which particle of medium are spread out is called rarefaction.

4.Compression:

The portion of longitudinal wave in which particles of medium are close to each other is called compression. 

7. How an a body produce sound? Explain briefly.

Ans: A body can produce sound by beating or plucking its surface. By doing so we can see that the surface of the body are vibrating on disturbing. Therefore sound is produced by vibrating bodies and travel away from vibrating body.

8. What is pitch of sound? How is it related with the frequency of sound? Ans: Pitch of sound:

It is a property of sound which tells us how shrill or grave sound is pitch of sounds helps us to distinguish between sound of different frequencies, because pitch of sound is directly related with the frequency of sound. Children, girls, birds and whittling sound are shrill and have greater frequencies. While lion's roar, man, and dog sounds. are grave and have smaller frequencies. Hence large frequency sounds have larger pitch.

9.What is loudness of sound? Name the factors on which loudness of sound depend.

Ans:Loudness of Sound: Loudness of sound is the sensation produced by sound on our ears. This property helps us to distinguish between a soft sound and a louder sound. Following are some factor which

affect loudness of sound.

(1) Amplified of the waves. 

(2) Surface Area of sound source.

(3) Distance form sound source. 

(4) Sensitivity of Ear.

10. A mobile phone is vibrating in your hand and another mobile is vibrating on a table. Which will be producing louder sound and why?

Ans:A mobile phone vibrating on a table would produce louder sound than vibrating in our hand because these vibration, produces more vibration on the surface of table. Also the surface area of the table is greater than the hand therefore mobile vibrating on table will produce louder sound.

11. How can you hear echo?

Ans: Echo:

Echo is the repetition of sound due to reflection of sound waves from a hard surface. Hence, when we speak in a big empty hall or shout towards hard wall a hill, the sound reflected back and after some time we hear echo. We can hear echo when the time gap b/w original sound and reflected it at least 0.1 sec and reflecting surface should be at least 17 meters.

12. In a cricket ground, batsman hits four in a test match. You notice that hitting sound of the bat is heard slightly after you see the bat actually hitting the ball. Why is it so?

Ans:We have noticed that hitting sound of the bat is heard slightly after we see that bat actually hitting the ball, this is due to the slow speed of sound in air. The hitting of a bat is faster than that of sound, therefore, the sound reaches us slightly later.aster than that of sound, therefore, the sound reaches us slightly later.