Question Answers For All Chapters – General Science Class 7
Sound : Production of Sound
Exercise
1. Fill in the blanks:
(a) Sound is generated by the rhythmic vibration of any object.
(b) The frequency of sound is measured in Hertz (Hz).
(c) If amplitude of sound is decreased, its loudness also decreases.
(d) A medium is necessary for propagation of sound.
2. Match the pairs:
| Group ‘A’ | Group ‘B’ |
|---|---|
| (a) Flute | (3) Vibrations in the air |
| (b) Frequency | (4) Measured in Hz |
| (c) Sound level | (5) Decibel |
| (d) Ultrasonic sound | (2) Frequency more than 20,000 Hz |
| (e) Infrasonic sound | (1) Frequency less than 20 Hz |
3. Give Scientific Reasons:
(a) In earlier times, people used to listen for the arrival of a distant train by putting their ear to the rail.
→ Sound travels faster in solids than in air. The railway track carries sound more efficiently, helping people hear the train earlier.
(b) The sounds generated by a tabla and a sitar are different.
→ Tabla produces low-pitched beats, while sitar produces high-pitched musical notes. The difference is due to the vibration of different materials and the way they are played.
(c) If you were both on the moon, your friend would not be able to hear you call.
→ Sound requires a medium (air, water, or solid) to travel, but there is no air on the moon, so sound cannot be transmitted.
(d) We can hear the movement of a mosquito’s wings but we cannot hear the movement of our hands.
→ The mosquito’s wings vibrate at a high frequency (above 200 Hz), which falls within the human hearing range, while our hands move at a very low frequency (below 20 Hz), which is inaudible.
4. Write answers to the following questions:
(a) How is sound produced?
→ Sound is produced when an object vibrates. These vibrations create waves in the surrounding air, water, or solids, which reach our ears and allow us to hear the sound.
(b) What does the intensity of sound depend upon?
→ The intensity of sound depends on its amplitude. A higher amplitude produces a louder sound, while a lower amplitude produces a softer sound.
(c) Explain how the frequency of oscillation is related to the length of a pendulum and the amplitude of its oscillation.
→ The longer the pendulum, the lower the frequency, meaning it oscillates slowly. The amplitude does not affect the frequency; it only affects how far the pendulum moves.
(d) Explain the two ways by which the pitch of the sound generated by a stretched string can be changed.
→ (1) Changing the tension: Higher tension increases frequency, producing a higher pitch.
→ (2) Changing the length of the string: A shorter string vibrates faster, creating a higher-pitched sound.
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