NCERT Class VIII Science Solutions: Chapter 13-Sound Part 2

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Question 7:

The loudness of sound is determined by the

  1. Amplitude of vibration

  2. Ratio of amplitude and frequency of vibration

  3. Frequency of vibration

  4. Product of amplitude and frequency of vibration

Answer: A

Image of amplitude of sound waves

Image of Amplitude of Sound Waves

Image of amplitude of sound waves

Question 8:

1 hertz is equal to

  1. 1 vibration per minute

  2. 10 vibrations per minute

  3. 60 vibrations per minute

  4. 600 vibrations per minute

Answer: C

Question 9:

Pitch of sound is determined by its

  1. Frequency

  2. Amplitude

  3. Speed

  4. Loudness

Answer: A

Image of sound wave

Image of Sound Wave

Image of sound wave

Question 10:

Ultrasound has frequency of vibration

  1. Between 20 to 20000Hz

  2. Below 20Hz

  3. Above 20000 Hz

  4. Between 500 and 10000 Hz

Answer: C

VERY SHORT ANSWER QUESTIONS

Question 11:

Lightning can be seen the moment it occurs. Paheli observes lightning in her area. She hears the sound after she observed lightning. How far is she from the place where lightning occurs?

Answer:

We know that

So, she is standing at 1.65 km from the place where lightning occurs.

Question 12:

Does any part of our body vibrate when we speak? Name the part.

Answer:

Yes, while speaking the part which vibrates is called vocal cords. It is below the throat and creates vibrations while speaking.

Question 13:

Boojho saw a cracker burst at night at a distance from his house. He heard the sound of the cracker a little later after seeing the cracker burst. Give reason for the delay in hearing the sound.

Answer:

The speed of sound is lower than that of the speed of light and therefore sound reaches him later than light.

Question 14:

When we hear a sound, does any part of our body vibrate? Name the part.

Answer:

Yes, it is the eardrum which vibrates and sends vibrations to the inner ear, when we hear any sound.

Question 15:

Name two musical instruments which produce sound by vibrating strings?

Answer:

Sitar and Ektara (any other musical instruments which produces sound by a vibrating string)

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