Quiz: Waves and Sound
Test your understanding of waves and sound with these 10 questions.
1. What is a wave?
- A moving object
- A disturbance that transfers energy through a medium or space
- A periodic force
- A type of oscillation in an object
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The correct answer is B. A wave is a disturbance that travels through a medium (like water or air) or through space (like light), transferring energy from one place to another. The medium itself oscillates but does not travel with the wave. Waves can be mechanical (requiring a medium) or electromagnetic (traveling through space).
Concept Tested: Wave Properties
2. How are wavelength and frequency related?
- Wavelength increases when frequency increases
- Wavelength and frequency are independent
- Wavelength decreases when frequency increases; they are inversely related
- Their relationship depends on the medium
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The correct answer is C. For waves in a given medium, v = fλ, where v is wave speed, f is frequency, and λ is wavelength. Since v is fixed for a medium, frequency and wavelength are inversely related: higher frequency means shorter wavelength. Light, for example, has higher frequency than radio waves and shorter wavelength.
Concept Tested: Wavelength
3. What causes the Doppler Effect?
- The wind blowing waves
- The relative motion between a wave source and observer
- The amplitude of the wave
- The wavelength of the source
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The correct answer is B. The Doppler Effect occurs when a source of waves moves relative to an observer. If the source approaches, wave crests bunch together, increasing observed frequency and pitch. If the source recedes, wavelength appears longer and frequency decreases. This is why ambulance sirens change pitch as they pass.
Concept Tested: Doppler Effect
4. An observer hears a siren frequency of 1200 Hz from an approaching ambulance. When the ambulance moves away, the frequency drops to 800 Hz. What is the actual source frequency?
- 800 Hz
- 1000 Hz
- 1200 Hz
- 2000 Hz
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The correct answer is B. The actual frequency is between observed frequencies: (1200 + 800)/2 = 1000 Hz. This uses the approximation for the Doppler effect when source velocity is much less than wave velocity. More precisely, the true frequency can be found using the Doppler formula for sound.
Concept Tested: Doppler Effect
5. What is the relationship between sound intensity and distance from the source?
- Intensity is constant regardless of distance
- Intensity is inversely proportional to distance squared
- Intensity decreases linearly with distance
- Intensity increases with distance
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The correct answer is B. Sound intensity follows the inverse square law: I ∝ 1/r². As distance doubles, intensity decreases to 1/4. This is because sound energy spreads over an increasingly large spherical surface area (A = 4πr²). This is why sound from distant thunder is much quieter than nearby lightning.
Concept Tested: Sound Intensity
6. What happens when two waves interfere constructively?
- The waves cancel each other
- The resulting wave has greater amplitude than either individual wave
- One wave destroys the other
- The waves pass through unchanged
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The correct answer is B. When two waves of the same frequency meet in phase (crests align with crests), they interfere constructively, resulting in a wave of greater amplitude. When they meet out of phase (crests align with troughs), they interfere destructively, reducing amplitude. This principle is used in noise-canceling headphones.
Concept Tested: Interference
7. A sound wave travels through air at 340 m/s with a frequency of 440 Hz. What is its wavelength?
- 0.77 m
- 0.95 m
- 1.3 m
- 2.5 m
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The correct answer is A. Using v = fλ: λ = v/f = 340 m/s ÷ 440 Hz ≈ 0.77 m. This is the wavelength of the musical note A (concert pitch). Longer wavelengths correspond to lower frequencies.
Concept Tested: Wavelength
8. What is diffraction?
- The bending of waves around obstacles
- The bouncing of waves off surfaces
- The combination of two waves
- The change in wave frequency
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The correct answer is A. Diffraction is the bending of waves around obstacles or through openings. It's most noticeable when the obstacle or opening is comparable to the wavelength. This is why you can hear sound around corners (long wavelengths diffract easily), but see shadows in straight lines (light has short wavelengths, minimal diffraction).
Concept Tested: Diffraction
9. What are harmonics in a vibrating string?
- Different types of wood used for the string
- Standing wave patterns with frequencies that are integer multiples of the fundamental frequency
- The amplitude of vibration
- The speed of wave propagation
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The correct answer is B. Harmonics are standing wave patterns where resonant frequencies are integer multiples of the fundamental (first harmonic). A string can vibrate at f, 2f, 3f, etc. These create the different timbres we hear in musical instruments—different combinations of harmonics give each instrument its characteristic sound.
Concept Tested: Harmonics
10. Why does a vibrating tuning fork create sound waves in air?
- The tuning fork pushes air out of the way
- The vibrating prongs create pressure variations that propagate as sound waves
- The tuning fork heats the surrounding air
- Sound waves come from friction with the air
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The correct answer is B. As the tuning fork prongs vibrate, they alternately compress and rarefy the air, creating pressure waves that propagate outward as sound. These pressure variations are what your ear detects and interprets as sound. The speed depends on air temperature and composition.
Concept Tested: Wave Properties