1. Define sound.
Sound is a form of energy carried by waves of vibrating particles. These waves can travel through soilds, liquids and gases. Sound cannot travel in vaccum. It requires a medium to travel.

2. Give two examples to show that sound is produced due to the vibration of objects.

• When a guitar is played, its strings are disturbed and produce vibrations in the instrument.
• Take a plastic scale and place it on a table so that some part of it projects out from the edge of the table. Place a heavy book on the other end of the ruler. Press the projecting end down with our fingers and release it. It will find that ruler will vibrate and produce sound.

3. Explain why sound requires a medium to propogate?
Some forms of energy require a medium to travel. Sound is one of them, for which the medium air is necessary. Since a vibrating object passes the vibrations to the air molecules,it means that the sound travels in a medium.

4. In which medium sound travels faster. Why?
Sound travels faster in denser medium. Sound travels faster through the soilds since it is denser. Sound travels little slower through liquids and comparitively slower through the gases or air.

5. Give an example to show that sound travels faster through the soilds.
Take a long metal rod kept it on a table. Bring your ear close to one end of the rod and strike the other end by a hammer. We hear the sound two times. First through metal rod and second time through the air. Then we concluded that sound travels faster through the soild.

6. Give an example to show that sound propagates in all direction.
Sound is a kind of energy which propagates in all directions. For example, when the school bell rings, we hear the sound no matter wherever we are in the campus of our school. If the observer is to the left of the bell or to the right of the bell, he can hear the sound. Hence we say that sound propagates in all possible directions through a medium.

7. Which is the unit of sound?
The loudness of sound is measured on a special scale called the decibel scale.
1db - One-tenth of bel, where bel is the unit of loudness level.

8. Which sound travels faster------- the roaring sound of a lion or the buzzing sound of a mosquito? why?
The buzzing sound of a mosquito travels faster because the frequency of buzzing of mosquito is more than that of a lion.
i.e., velocity of sound = frequecy x wavelength

9. Define musical sound.
Musical sound is that sound which pleases our ears. It is produced by schematic periodic vibrations. Example: Sound produced by musical instruments.

10. Define Noise. Give an example.
When sound produced by a source is not pleasant to our ears, it is called noise. It occurs due to irregular vibrations by the sources.
Example: Sound produced by different machines.

11. Write two difference between noise and music.
Noise:

• Noise is produced by irregular vibrations.
• It cannot be reproduce.

Music:

• It is produced by notes having definite frequencies.
• It can be reproduce.

12. What are the sources of sound?

1. Tuning fork
2. Musical Instruments
3. Human sound

13. Explain the structure of tuning fork.
It is a U-shaped metallic instrument having a stem between the two prongs. The stem is taken in the hand and the prongs are bit on the rubber pad. The prongs vibrate and produce frequency. The frequency of each tuning forks are written on their stem.

14. Write names of some musical instrument.
There are several types of musical instrument which produce sound. For example, stringed instruments, percussion instruments, wind instrument etc.

15. Define Reed Instruments.
The harmonium and the mouth-organ are called reed instruments. These instruments have metal reeds which produce sound when air is blown through them.

16. Which types of instruments are called Wind Instrument?Give two examples.
Wind instrument are generally the instruments having a pipelike structure. When you blow through one end, air inside the instrument vibrates and thus produces a note.
Eg: Flute, bugle,trumpet etc.

17. What are vocal cords?
Our throat has a larynx. The voice is produced in the larynx. Larynx is also called the voice box. It is designed to produce voice. It is a box like structure with walls of tough tissues. Inside two folds of the tissue, there is a gap inside two folded tissues. They are the vocal chords.