NCERT Class VIII Science Solutions: Chapter 13-Sound Part 1

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Question 1:

Choose the correct answer: Sound can travel through.

  1. Gases only

  2. Solids only

  3. Liquids only

  4. Solids, liquids and gases.

Answer:

Sounds are carried by vibrating particles.

Sound can travel through: Solids (Air in the room), liquids (water in a swimming pool) and gases (walls and windows).

Sounds cannot travel through a vacuum (totally empty space).

This image shows sound can travel through solids and liquids but not a vacuum

Sound Can Travel through Solids and Liquids but Not a Vacuum

This image shows sound can travel through solids and liquids but not a vacuum

Question 2:

Which of the following voices is likely to have minimum frequency?

  1. Baby girl

  2. Baby boy

  3. A man

  4. A woman

Answer:

C. A man

Frequency of a sound is directly proportional to its pitch and inversely proportional to its amplitude. The voice of an adult man is of lower pitch and high amplitude in comparison to the voices of a baby boy, a baby girl and a woman. The voice of a baby girl has highest pitch among this group.

Question 3:

In the following statements, tick T against those which are true, and F against those which are false:

  1. Sound cannot travel in vacuum. (T/F)

  2. The number of oscillations per second of a vibrating object is called its time period. (T/F)

  3. If the amplitude of vibration is large, sound is feeble. (T/F)

  4. For human ears, the audible range is (T/F)

  5. The lower the frequency of vibration, the higher is the pitch. (T/F)

  6. Unwanted or unpleasant sound is termed as music. (T/F)

  7. Noise pollution may cause partial hearing impairment. (T/F)

Answer:

  1. Sound cannot travel in vacuum. (True)

  2. The number of oscillations per second of a vibrating object is called its time period. (False)

  3. If the amplitude of vibration is large, sound is feeble. (False)

  4. For human ears, the audible range is (True)

  5. The lower the frequency of vibration, the higher is the pitch. (False)

  6. Unwanted or unpleasant sound is termed as music. (False)

  7. Noise pollution may cause partial hearing impairment. (True)

Question 4:

Fill in the blanks with suitable words.

  1. Time taken by an object to complete one oscillation is called....................

  2. Loudness is determined by the ......................... of vibration.

  3. The unit of frequency is.......................... .

  4. Unwanted sound is called..........................

  5. Shrillness of a sound is determined by the................. Of vibration.

Answer:

  1. Time taken by an object to complete one oscillation is called time period.

  2. Loudness is determined by the amplitude of vibration.

Image result for amplitude

Amplitude

Image result for amplitude

  1. The unit of frequency is hertz (Hz).

  2. Unwanted sound is called noise.

  3. Shrillness of a sound is determined by the frequency of vibration.