Sound travels fastest in steel and cannot travel through a vacuum, so this Class 9 sheet opens with the fastest medium and the missing one. The key records hertz for frequency, the 20 Hz to 20 kHz range and 340 m/s for the air speed.
Key Takeaways
Sound travels fastest in steel (Q1).
Sound cannot travel through a vacuum (Q2).
Q3 records hertz as the frequency unit.
Section A: Multiple Choice Questions (1 Mark Each)
Choose the correct option for each question.
1.Sound travels fastest in
(a) air(b) water(c) steel(d) vacuum
2.Sound cannot travel through
(a) solids(b) liquids(c) gases(d) vacuum
3.What is the SI unit of frequency?
(a) hertz(b) decibel(c) metre(d) pascal
4.The audible frequency range for the human ear is
(a) 20 Hz to 20 kHz(b) 20 Hz to 2000 Hz(c) 1 Hz to 20 Hz(d) 20 kHz to 20 MHz
5.The repeated reflection of sound that results in its persistence is called
(a) resonance(b) reverberation(c) echo(d) noise
6.The speed of sound in air at room temperature is approximately
(a) 340 m/s(b) 1500 m/s(c) 3 × 10⁸ m/s(d) 34 m/s
Section B: Short Answer Type Questions (2 Marks Each)
Show all steps clearly.
7.What kind of waves are sound waves in air?
8.Define frequency and state its SI unit.
9.What is an echo? Which property of sound is responsible for an echo?
10.Why do astronauts use radio devices to talk to each other on the Moon?
11.Distinguish between infrasound and ultrasound.
12.State the relation between the speed, frequency and wavelength of a wave.
13.Why is sound called a mechanical wave?
14.What is the range of frequencies audible to the human ear?
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 400 Hz and a wavelength of 0.85 m. Find the speed of sound. (v = fλ)
16.The speed of sound in air is 340 m/s. Find the wavelength of a note of frequency 512 Hz. (λ = v ÷ f)
17.A person 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 from the person. (Distance = speed × time ÷ 2)
18.A wave has a time period of 0.02 s. Find its frequency. (f = 1 ÷ T)
19.A source produces 600 compressions and rarefactions in 2 minutes. Find the frequency of the wave. (Frequency = number of waves ÷ time)
20.Sound takes 4 seconds to travel a distance of 1360 m in air. Find the speed of sound. (Speed = distance ÷ time)
Answer Key
1. c) steel
2. d) vacuum
3. a) hertz
4. a) 20 Hz to 20 kHz
5. b) reverberation
6. a) 340 m/s
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End of Worksheet
People Also Ask
Where does sound travel fastest?
In steel, option (c) in this worksheet (Q1).
What can sound not travel through?
A vacuum, option (d) in this worksheet (Q2).
What is the audible frequency range?
20 Hz to 20 kHz, option (a) in this worksheet (Q4).
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