Sound - Exemplar Solutions 2

CBSE Class 8 Science
NCERT Exemplar Solutions

11. Lightning can be seen the moment it occurs. Paheli observes lightning in her area. She hears the sound 5 s after she observed lightning. How far is she from the place where lightning occurs? (Speed of sound = 330 m/s)
Ans: Speed of sound = 330 m/s i.e. distance travelled by light in 1 s is 330 m.
Therefore, distance covered by light in 5 s will be 330 x 5 = 1650 m.
Paheli is 1650 m away from the place of lightning.

12. Does any part of our body vibrate when we speak? Name the part.
Ans: Yes, the part of our body that vibrates when we speak is the larynx (also known as vocal cords)

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.
Ans: Reason for the delay is the difference between the speed of sound and the speed of light. The speed of sound is lower than the speed of light. The light of the cracker burst travelled faster than the sound of the cracker. Therefore, Boojho heard the sound of the cracker a little later after seeing the cracker burst.

14. When we hear a sound, does any part of our body vibrate? Name the part.
Ans: The vibrations of a sound that reach our ears vibrate the eardrum.
Explanation: The eardrum in turn sends the vibrations to the inner ear. The inner ear sends the signal to the brain and that is how, we are able to hear the sound.

15. Name two musical instruments which produce sound by vibrating strings?
Ans: Sitar and Ektara are two musical instruments which produce sound by vibrating strings.