Physics Practice Test: Waves and Sound
- Waves and Sound
- 10 questions
- 15 minutes
These 10 questions cover wave properties and sound. Take the speed of sound in air from each question. The key equation is v = fλ: the medium sets the speed, the source sets the frequency, and the wavelength follows from both.
Tap an option to mark your answer. You can change your mind, or tap the same option again to leave the question blank. The correct answers and explanations appear when you finish the test.Tap an option to answer; tap it again to leave the question blank.
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Question 1
A sound wave in air has a frequency of 680 Hz. The speed of sound is 340 m/s. What is its wavelength?
Correct answer: D
λ = v/f = 340/680 = 0.50 m. 2.0 m divides frequency by speed, which flips the relationship.
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Question 2
A wave has a frequency of 25 Hz. What is its period?
Correct answer: A
T = 1/f = 1/25 = 0.040 s. 25 s mixes up period and frequency, which are reciprocals of each other.
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Question 3
Which statement correctly describes a sound wave traveling through air?
Correct answer: C
Sound in air is a series of compressions and rarefactions, so the particles move back and forth along the wave's direction. The molecules oscillate in place; energy travels, not the air itself.
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Question 4
A hiker shouts toward a cliff and hears the echo 1.2 s later. The speed of sound is 343 m/s. How far away is the cliff?
Correct answer: B
In 1.2 s the sound travels 343 × 1.2 ≈ 412 m, but that is there and back, so the cliff is about 206 m away. 412 m forgets the round trip.
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Question 5
A musician plays the same note louder. Which property of the sound wave increases?
Correct answer: C
Loudness depends mainly on amplitude, while pitch depends on frequency. Since the note is the same, its frequency and wavelength do not change, and the speed is set by the air.
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Question 6
An ambulance with its siren on drives toward you and then past you. What do you hear?
Correct answer: B
This is the Doppler effect: the waves are bunched up in front of a moving source and stretched out behind it. The siren's own frequency never changes; only the frequency you receive does.
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Question 7
A guitar string 0.60 m long is fixed at both ends. Waves travel along it at 240 m/s. What is its fundamental frequency?
Correct answer: D
The fundamental has λ = 2L = 1.2 m, so f = v/λ = 240/1.2 = 200 Hz. 400 Hz uses λ = L, which is the second harmonic.
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Question 8
A pipe 0.85 m long is closed at one end and open at the other. The speed of sound is 340 m/s. What is the pipe's fundamental frequency?
Correct answer: A
A pipe closed at one end has λ = 4L = 3.4 m for its fundamental, so f = 340/3.4 = 100 Hz. 200 Hz uses λ = 2L, which applies to a pipe open at both ends.
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Question 9
The sound level near a machine rises from 70 dB to 80 dB. By what factor does the sound intensity increase?
Correct answer: D
Each 10 dB step on the decibel scale means 10 times the intensity. The scale is logarithmic, so 80 dB is not just 80/70 ≈ 1.14 times as intense.
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Question 10
Two tuning forks with frequencies of 440 Hz and 444 Hz are struck at the same time. What beat frequency do you hear?
Correct answer: C
The beat frequency is the difference of the two frequencies: 444 − 440 = 4 Hz. 442 Hz is the average, which is the pitch you hear, not the beat rate.
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