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Physics Chapter 9 : Topic 2
Doppler Effect
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The Doppler Effect is the phenomenon in which:
Reasoning: The Doppler Effect is the apparent change in frequency due to relative motion between source and observer.
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The Doppler Effect is produced when:
Reasoning: The topic specifically considers a moving sound source and a stationary observer.
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When a sound source approaches a stationary observer, the observed frequency:
Reasoning: Approaching source causes wave fronts to become closer, increasing observed frequency.
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When a sound source moves away from a stationary observer, the observed frequency:
Reasoning: Receding source produces stretched wavefronts, reducing observed frequency.
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The actual frequency produced by the source is called:
Reasoning: Source frequency is the frequency emitted by the vibrating source.
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When a sound source moves toward a listener, the distance between successive wavefronts:
Reasoning: The moving source compresses wavefronts in front of it.
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The wavelength of sound decreases in front of an approaching source because:
Reasoning: The source moves closer to each new wavefront, reducing wavelength.
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For a source moving away from an observer, the wavelength in front of the observer:
Reasoning: The source moves away, increasing the separation between wavefronts.
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During Doppler Effect, the speed of sound in the medium:
Reasoning: The speed of sound depends on the medium, not on the motion of the source.
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A moving source changes the observed frequency mainly by changing:
Reasoning: Since $\mathbf{v = f\lambda}$, a change in wavelength changes the observed frequency.
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For a source moving toward a stationary observer, the observed frequency is given by:
Reasoning: For an approaching source $\mathbf{\Longrightarrow}$ $\mathbf{f}^{\mathbf{'}}\mathbf{= f}$ $\left( \frac{\mathbf{v}}{\mathbf{v\ - \ }\mathbf{v}_{\mathbf{s}}} \right)$
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The Doppler Effect occurs because the source motion changes:
Reasoning: The source frequency remains constant, but wavelength received changes.
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For a source moving away from a stationary observer, the observed frequency is:
Reasoning: Receding source increases wavelength and lowers frequency.
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A sound source of frequency $\mathbf{500\ Hz}$ approaches an observer. The observer hears:
Reasoning: Approaching motion increases apparent frequency.
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A car horn sounds lower in pitch after the car passes a person because:
Reasoning: After passing, the source recedes and observed frequency decreases.
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A source produces sound of frequency $\mathbf{400\ Hz}$. If the observer hears a higher frequency, the source is most likely:
Reasoning: Approaching source produces increased observed frequency.
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A source emits sound at $\mathbf{600\ Hz}$ and moves away from a stationary observer. The observed frequency may be:
Reasoning: A receding source produces a lower observed frequency.
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A police siren appears to change pitch as the vehicle passes because:
Reasoning: The Doppler Effect causes apparent frequency changes.
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A source moving toward an observer with increasing speed will produce:
Reasoning: Greater source speed causes greater wavefront compression.
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A stationary observer hears a lower frequency from a moving source because:
Reasoning: A receding source creates longer wavelengths.
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Which quantity remains unchanged during the Doppler effect?
Reasoning: The source continues vibrating at its original frequency.
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The pitch of sound depends on:
Reasoning: Higher frequency means higher pitch.
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A moving source does not change the sound speed because:
Reasoning: Sound speed is determined by properties of the medium.
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The Doppler Effect is observed for sound because sound waves are:
Reasoning: Sound requires a medium for propagation.
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If a sound source moves faster toward an observer, the wavefronts become:
Reasoning: Higher source speed produces greater compression of waves.
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A source moving with constant velocity produces sound. A stationary observer notices a constant higher frequency. The source is:
Reasoning: Constant higher frequency indicates uniform approach.
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If a source moves away from a stationary observer with increasing speed, the observed frequency:
Reasoning: Increasing speed of recession causes greater wavelength stretching.
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The Doppler Effect does not mean that:
Reasoning: The source frequency remains unchanged; only observed frequency changes.
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Two observers hear different frequencies from the same moving source because:
Reasoning: Different relative motion causes different observed frequencies.
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The best explanation of Doppler effect for a moving source is:
Reasoning: Source motion changes wavelength received, causing a change in apparent frequency.
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