AP Physics 2 Flashcards: The Doppler Effect

What this deck covers

This deck focuses on The Doppler Effect, giving you a quick way to review the definitions, rules, and examples that matter most for AP Physics 2.

How to use these flashcards

Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: Does the Doppler Effect occur in a vacuum?

Answer: Yes, for electromagnetic waves. Light waves don't need a medium, so the effect still occurs in space.

Flashcard 2: Which color shift indicates an object is moving towards the observer?

Answer: Blueshift. Shorter wavelengths appear bluer, indicating approach toward the observer.

Flashcard 3: In the Doppler Effect, what happens to frequency as the source moves away?

Answer: Frequency decreases. Receding motion stretches wavefronts, creating lower frequency.

Flashcard 4: How does the speed of sound affect the Doppler Effect?

Answer: Higher speed reduces effect. Higher wave speed in the denominator reduces the fractional frequency change.

Flashcard 5: What is the Doppler Effect?

Answer: The change in frequency or wavelength due to relative motion. This fundamental phenomenon occurs when there's relative motion between source and observer.

Flashcard 6: State the formula for the Doppler shift in light.

Answer: $\Delta \lambda = \lambda_o \frac{v}{c}$. For light, the shift is proportional to velocity divided by light speed.

Flashcard 7: What are the units of frequency in the Doppler Effect?

Answer: Hertz (Hz). Frequency measures cycles per second, the standard unit for wave oscillations.

Flashcard 8: State the formula for the Doppler shift in light.

Answer: $\Delta \lambda = \lambda_o \frac{v}{c}$. For light, the shift is proportional to velocity divided by light speed.

Flashcard 9: Which principle explains the Doppler Effect?

Answer: Wavefronts moving relative to an observer. Relative motion changes the spacing between successive wavefronts.

Flashcard 10: How do you calculate the speed of an object using the Doppler Effect?

Answer: Use observed frequency shift. Rearrange the Doppler formula to solve for unknown velocity.

Flashcard 11: What happens to wavelength during a blueshift?

Answer: Wavelength decreases. Higher frequency corresponds to shorter wavelength in electromagnetic waves.

Flashcard 12: What happens to wavelength during a blueshift?

Answer: Wavelength decreases. Higher frequency corresponds to shorter wavelength in electromagnetic waves.

Flashcard 13: How is the Doppler Effect used in medical imaging?

Answer: Measures blood flow velocity. Ultrasound waves reflect off moving blood cells to measure flow rates.

Flashcard 14: Calculate $f'$ when $f = 600$ Hz, $v = 343$ m/s, $v_o = 5$ m/s, $v_s = 5$ m/s.

Answer: Observed frequency $f' = 600$ Hz. Equal speeds in opposite directions: $f' = 600 \times \frac{348}{348} = 600$ Hz.

Flashcard 15: What is the observed frequency when source and observer are stationary?

Answer: Observed frequency equals source frequency. No relative motion means no change in wavefront spacing or frequency.

Flashcard 16: What happens to wavelength during a redshift?

Answer: Wavelength increases. Lower frequency corresponds to longer wavelength in electromagnetic waves.

Flashcard 17: What are the units of frequency in the Doppler Effect?

Answer: Hertz (Hz). Frequency measures cycles per second, the standard unit for wave oscillations.

Flashcard 18: Identify $f$ in the Doppler Effect formula.

Answer: Source frequency. The original frequency emitted by the source before any Doppler shift.

Flashcard 19: What does $v_o$ represent in the Doppler Effect formula?

Answer: Speed of the observer. Positive when observer moves toward source, negative when moving away.

Flashcard 20: If $v_o = v_s$, what is the effect on the observed frequency?

Answer: No effect on frequency. Equal and opposite velocities cancel out, producing no net Doppler shift.

Flashcard 21: How does the Doppler Effect influence the pitch of a car horn?

Answer: Pitch is higher when approaching. Approaching vehicles create higher pitch, receding vehicles create lower pitch.

Flashcard 22: Calculate observed frequency: $f = 500$ Hz, $v = 340$ m/s, $v_o = 10$ m/s, $v_s = 0$ m/s.

Answer: Observed frequency $f' = 515$ Hz. Observer moving toward stationary source: $f' = 500 \times \frac{350}{340} = 515$ Hz.

Flashcard 23: What is the observed frequency when source and observer are stationary?

Answer: Observed frequency equals source frequency. No relative motion means no change in wavefront spacing or frequency.

Flashcard 24: Which color shift indicates an object is moving away from the observer?

Answer: Redshift. Longer wavelengths appear redder, indicating recession from the observer.

Flashcard 25: Which direction does frequency shift if observer moves away from the source?

Answer: Frequency decreases. Observer motion away from source stretches received wavefronts.

Flashcard 26: What is a practical application of the Doppler Effect in law enforcement?

Answer: Speed radar guns. Police use Doppler radar to measure vehicle speeds for traffic enforcement.

Flashcard 27: What does $v_s$ represent in the Doppler Effect formula?

Answer: Speed of the source. Positive when source moves toward observer, negative when moving away.

Flashcard 28: How is the Doppler Effect used in medical imaging?

Answer: Measures blood flow velocity. Ultrasound waves reflect off moving blood cells to measure flow rates.

Flashcard 29: How does the speed of sound affect the Doppler Effect?

Answer: Higher speed reduces effect. Higher wave speed in the denominator reduces the fractional frequency change.

Flashcard 30: Calculate observed frequency: $f = 500$ Hz, $v = 340$ m/s, $v_o = 10$ m/s, $v_s = 0$ m/s.

Answer: Observed frequency $f' = 515$ Hz. Observer moving toward stationary source: $f' = 500 \times \frac{350}{340} = 515$ Hz.

Flashcard 31: Which direction does frequency shift if observer moves towards the source?

Answer: Frequency increases. Observer motion toward source compresses received wavefronts.

Flashcard 32: What does $v_s$ represent in the Doppler Effect formula?

Answer: Speed of the source. Positive when source moves toward observer, negative when moving away.

Flashcard 33: What effect does the Doppler Effect have on light from receding galaxies?

Answer: Redshift. Light from objects moving away shifts toward longer, redder wavelengths.

Flashcard 34: When does the Doppler Effect produce no change in frequency?

Answer: When source and observer have no relative motion. Zero relative velocity produces no wavefront compression or stretching.

Flashcard 35: What type of wave does the Doppler Effect apply to?

Answer: Sound and light waves. The effect occurs for all wave phenomena including mechanical and electromagnetic waves.

Flashcard 36: How is the Doppler Effect used in astronomy?

Answer: Measures star velocities. Spectral line shifts reveal whether stars are approaching or receding.

Flashcard 37: In the Doppler Effect, what happens to frequency as the source approaches?

Answer: Frequency increases. Approaching motion compresses wavefronts, creating higher frequency.

Flashcard 38: State the formula for the Doppler Effect for sound.

Answer: $f' = f \frac{v + v_o}{v + v_s}$. Observer velocity is positive when moving toward source, source velocity positive when moving toward observer.

Flashcard 39: What is a practical application of the Doppler Effect in law enforcement?

Answer: Speed radar guns. Police use Doppler radar to measure vehicle speeds for traffic enforcement.

Flashcard 40: Calculate observed frequency: $f = 400$ Hz, $v = 340$ m/s, $v_o = 0$ m/s, $v_s = 20$ m/s.

Answer: Observed frequency $f' = 377$ Hz. Source moving away from stationary observer: $f' = 400 \times \frac{340}{360} = 377$ Hz.

Flashcard 41: When does the Doppler Effect produce no change in frequency?

Answer: When source and observer have no relative motion. Zero relative velocity produces no wavefront compression or stretching.

Flashcard 42: How do you calculate the speed of an object using the Doppler Effect?

Answer: Use observed frequency shift. Rearrange the Doppler formula to solve for unknown velocity.

Flashcard 43: What does $c$ represent in the Doppler shift formula for light?

Answer: Speed of light in vacuum. The universal constant approximately $3.0 \times 10^8$ m/s.

Flashcard 44: What does $\Delta \lambda$ represent in the Doppler shift formula for light?

Answer: Change in wavelength. This represents the difference between observed and original wavelength.

Flashcard 45: What does $v_o$ represent in the Doppler Effect formula?

Answer: Speed of the observer. Positive when observer moves toward source, negative when moving away.

Flashcard 46: What happens to wavelength during a redshift?

Answer: Wavelength increases. Lower frequency corresponds to longer wavelength in electromagnetic waves.

Flashcard 47: What does $v$ represent in the Doppler Effect formula?

Answer: Speed of sound in the medium. This constant depends on the medium's properties and temperature.

Flashcard 48: What effect does the Doppler Effect have on light from approaching galaxies?

Answer: Blueshift. Light from objects moving closer shifts toward shorter, bluer wavelengths.

Flashcard 49: What does $c$ represent in the Doppler shift formula for light?

Answer: Speed of light in vacuum. The universal constant approximately $3.0 \times 10^8$ m/s.

Flashcard 50: What type of wave does the Doppler Effect apply to?

Answer: Sound and light waves. The effect occurs for all wave phenomena including mechanical and electromagnetic waves.

Flashcard 51: Which color shift indicates an object is moving away from the observer?

Answer: Redshift. Longer wavelengths appear redder, indicating recession from the observer.

Flashcard 52: Calculate observed frequency: $f = 400$ Hz, $v = 340$ m/s, $v_o = 0$ m/s, $v_s = 20$ m/s.

Answer: Observed frequency $f' = 377$ Hz. Source moving away from stationary observer: $f' = 400 \times \frac{340}{360} = 377$ Hz.

Flashcard 53: State the formula for the Doppler Effect for sound.

Answer: $f' = f \frac{v + v_o}{v + v_s}$. Observer velocity is positive when moving toward source, source velocity positive when moving toward observer.

Flashcard 54: How is the Doppler Effect used in astronomy?

Answer: Measures star velocities. Spectral line shifts reveal whether stars are approaching or receding.

Flashcard 55: What does $\lambda_o$ represent in the Doppler shift formula for light?

Answer: Observed wavelength. The wavelength measured by the observer after Doppler shifting.

Flashcard 56: Identify $f'$ in the Doppler Effect formula.

Answer: Observed frequency. This is the frequency detected by the observer after the Doppler shift occurs.

Flashcard 57: If $v_o = v_s$, what is the effect on the observed frequency?

Answer: No effect on frequency. Equal and opposite velocities cancel out, producing no net Doppler shift.

Flashcard 58: What effect does the Doppler Effect have on light from approaching galaxies?

Answer: Blueshift. Light from objects moving closer shifts toward shorter, bluer wavelengths.

Flashcard 59: What effect does the Doppler Effect have on light from receding galaxies?

Answer: Redshift. Light from objects moving away shifts toward longer, redder wavelengths.

Flashcard 60: What does $v$ represent in the Doppler Effect formula?

Answer: Speed of sound in the medium. This constant depends on the medium's properties and temperature.

Flashcard 61: Which direction does frequency shift if observer moves away from the source?

Answer: Frequency decreases. Observer motion away from source stretches received wavefronts.

Flashcard 62: In the Doppler Effect, what happens to frequency as the source approaches?

Answer: Frequency increases. Approaching motion compresses wavefronts, creating higher frequency.

Flashcard 63: In the Doppler Effect, what happens to frequency as the source moves away?

Answer: Frequency decreases. Receding motion stretches wavefronts, creating lower frequency.

Flashcard 64: Identify $f$ in the Doppler Effect formula.

Answer: Source frequency. The original frequency emitted by the source before any Doppler shift.

Flashcard 65: Identify $f'$ in the Doppler Effect formula.

Answer: Observed frequency. This is the frequency detected by the observer after the Doppler shift occurs.

Flashcard 66: Which color shift indicates an object is moving towards the observer?

Answer: Blueshift. Shorter wavelengths appear bluer, indicating approach toward the observer.

Flashcard 67: What does $\Delta \lambda$ represent in the Doppler shift formula for light?

Answer: Change in wavelength. This represents the difference between observed and original wavelength.

Flashcard 68: What does $\lambda_o$ represent in the Doppler shift formula for light?

Answer: Observed wavelength. The wavelength measured by the observer after Doppler shifting.

Flashcard 69: Which direction does frequency shift if observer moves towards the source?

Answer: Frequency increases. Observer motion toward source compresses received wavefronts.

Flashcard 70: Does the Doppler Effect occur in a vacuum?

Answer: Yes, for electromagnetic waves. Light waves don't need a medium, so the effect still occurs in space.

Flashcard 71: How does the Doppler Effect influence the pitch of a car horn?

Answer: Pitch is higher when approaching. Approaching vehicles create higher pitch, receding vehicles create lower pitch.

Flashcard 72: How does the Doppler Effect affect weather radar?

Answer: Detects motion of raindrops. Radar waves reflect off moving precipitation, showing velocity information.

Flashcard 73: What is the speed of sound in air at room temperature?

Answer: Approximately 343 m/s. This value varies slightly with temperature and humidity conditions.

Flashcard 74: Calculate $f'$ when $f = 600$ Hz, $v = 343$ m/s, $v_o = 5$ m/s, $v_s = 5$ m/s.

Answer: Observed frequency $f' = 600$ Hz. Equal speeds in opposite directions: $f' = 600 \times \frac{348}{348} = 600$ Hz.

Flashcard 75: How does the Doppler Effect affect weather radar?

Answer: Detects motion of raindrops. Radar waves reflect off moving precipitation, showing velocity information.

Flashcard 76: Which principle explains the Doppler Effect?

Answer: Wavefronts moving relative to an observer. Relative motion changes the spacing between successive wavefronts.