Sound is produced by vibration and sound cannot travel through a vacuum, so this Grade 8 sheet opens with the cause of sound and its medium limit. Hertz, the 20 Hz to 20000 Hz range and ultrasonic answers follow in the key.
Key Takeaways
Sound is produced by vibration (Q1).
Sound cannot travel through a vacuum (Q2).
Q5 records ultrasonic among the answers.
Section A: Multiple Choice Questions (1 Mark Each)
Choose the correct option for each question.
1.Sound is produced by:
(a) Vibration(b) Friction(c) Heat(d) Light
2.Sound cannot travel through:
(a) Air(b) Water(c) Vacuum(d) Steel
3.The SI unit of frequency is:
(a) Hertz(b) Decibel(c) Pascal(d) Newton
4.The audible range of frequency for human beings is:
(a) 20 Hz to 200 Hz(b) 20 Hz to 2000 Hz(c) 20 Hz to 20000 Hz(d) 200 Hz to 20000 Hz
5.Sound waves of frequency higher than 20,000 Hz are called:
(a) Infrasonic(b) Ultrasonic(c) Supersonic(d) Inaudible to all animals
6.The loudness of sound depends on its:
(a) Amplitude(b) Frequency(c) Wavelength(d) Speed
Section B: Short Answer Type Questions (2 Marks Each)
Show all steps clearly.
7.What is vibration? How does a vibrating object produce sound?
8.Why is sound not heard on the surface of the Moon even if two astronauts shout?
9.Differentiate between loudness and pitch of a sound.
10.What is an echo? What is the minimum distance between the source and the reflecting surface to hear a distinct echo?
11.Name two animals that can hear ultrasonic sounds.
12.What is the time period of a sound wave? How is it related to frequency?
13.Define frequency. Write its SI unit and give its relation with time period.
14.Why are the walls of a sound-proof room covered with soft, porous materials?
Section C: Numericals & Word Problems (3 Marks Each)
Apply the concepts to solve the problems. Show all working.
15.A sound wave has a frequency of 440 Hz. If the speed of sound in air is 344 m/s, find its wavelength.
16.A sound wave travels at 340 m/s and has a wavelength of 2 m. Calculate its frequency.
17.A man claps near a cliff and hears the echo after 2 seconds. If the speed of sound is 340 m/s, find the distance of the cliff.
18.The frequency of a sound wave is 50 Hz. Find its time period.
19.A vibrating source produces 600 vibrations in 3 seconds. Calculate the frequency of the sound produced.
20.A ship sends a sound signal downwards and receives its echo from the seabed after 1.5 seconds. If the speed of sound in water is 1500 m/s, find the depth of the sea.
Answer Key
1. a) Vibration
2. c) Vacuum
3. a) Hertz
4. c) 20 Hz to 20000 Hz
5. b) Ultrasonic
6. a) Amplitude
7. Refer to solution guide.
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End of Worksheet
People Also Ask
What produces sound?
Vibration, option (a) in this worksheet (Q1).
What can sound not travel through?
A vacuum, option (c) in this worksheet (Q2).
What is the audible frequency range?
20 Hz to 20000 Hz, option (c) in this worksheet (Q4).
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