When a car travelling with constant velocity passes a stationary observer, the observer hears a change in the frequency of sound emitted by the car. Which statement is correct ?
Correct answer: B. The greater the speed of the car, the greater the change in observed frequency.
- A. The change in frequency is greater as a car moves away than as it approaches.
- B. The greater the speed of the car, the greater the change in observed frequency.
- C. The observed frequency is lower as the car moves toward the observer and higher as the car moves away from the observer
- D. The volume of the sound heard by the observer does not change as the car approaches.
Explanation
Wave speed is the distance a wave travels in a given amount of time, such as the number of meters it travels per second. Wave speed is related to wavelength and wave frequency by the equation: Speed = Wavelength x Frequency so as the speed increases the observed frequency also increases.
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About Waves
Progressive waves transfer energy through oscillations, with wavelength, frequency, amplitude and wave speed related by v = fλ; sound speed depends on the medium. Superposition produces interference and stationary waves in strings and organ pipes, while simple harmonic motion describes the oscillation itself and must be distinguished from wave propagation.
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