Page 142 - Science Class 08

C. Fill in the blanks.
1. Sound always travels in waves made up of _________________ and _________________ .

2. The ______________________________ causes the three bones of middle ear to vibrate.
3. An obstacle in the way of a sound-wave makes it change its ____________________ .
4. There must be a gap of _________________ seconds between the original sound and its
reflected version.
5. Birds have no _________________ but syrinx to produce sounds.

D. Account for the following.
1. An echo needs a gap of 1/10 seconds between the original sound and its reflected version.
2. An echo needs an obstacle at a distance of at least 16.6 metres from the sound-source.
3. A bat squeaks with an ultrasonic sound to locate its prey.

4. A frog inflates its throat while croaking to amplify its sound.
5. Some birds can produce two sounds at a me.
E. Write the correct name for.

1. the object or creature that produces a sound : _________________________
2. the body-part that hears the sound : _________________________
3. the sense that is carried by ears : _________________________
4. the ear-part that links middle ear with inner ear : _________________________

5. the ear-part that amplifies the sound : _________________________
6. the animal that uses echo to locate its prey : _________________________
7. the instruments that have taut strings : _________________________

8. the water animal that inflates its : _________________________
throat while crying
F. Short answer ques ons.
1. What is the difference between sound and noise?

2. What is rarefrac on of air?
3. What is the func on of middle ear?
4. What helps birds to create sound?
5. How many kinds of musical sounds are there?

G. Long answer ques ons.
1. What is a sound-wave? How does it take shape? Explain through a clear diagram.
2. When does a reflected sound become an echo? Explain with a diagram.
3. How is a sound heard? Explain in steps through a clear diagram.

4. What is an echo? How can it help to measure the depth of an ocean?
5. Write how do noise and a musical sounds take shape? What is their main difference?
6. Write an essay on the various categories of musical instruments.

7. Write notes on:
(a) human voice (b) animal sounds (c) bird sounds

142 Science-8