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Doppler Effect (DP IB Physics)

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  • FrontThe Doppler Effect

    Define the Doppler effect.

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Cards in this collection (35)

  • Define the Doppler effect.

    The Doppler effect is the change in frequency due to the relative motion between a source of sound or light and an observer.

  • What happens to the frequency of a sound as the source moves away from a stationary observer?

    The frequency of a sound appears to decrease as the source moves away from a stationary observer.

  • True or False?

    The Doppler effect only applies to sound waves.

    False.

    The Doppler effect applies to both sound and electromagnetic waves.

  • How does the wavelength of a sound change when the source moves towards a stationary observer?

    The wavelength of a sound decreases when the source moves towards a stationary observer.

  • What happens in red shift?

    In red shift, electromagnetic waves shift to the red end of the spectrum as they move away from the observer.

  • What happens in blue shift?

    In blue shift, electromagnetic waves shift to the blue end of the spectrum as they move towards the stationary observer.

  • State the effect of the Doppler shift on light waves moving away from an observer.

    The effect of the Doppler shift on light waves moving away from an observer is that the light waves are red-shifted, meaning their wavelength increases and frequency decreases.

  • Use the Doppler effect to explain the change in pitch of an ambulance siren as it moves towards and then away from a stationary observer.

    As the ambulance moves towards a stationary observer:

    • the siren's pitch gets higher

    • because the frequency increases

    As the ambulance moves away from a stationary observer:

    • the siren's pitch gets lower

    • because the frequency decreases

  • Which phenomenon describes the decrease in wavelength as a source approaches an observer?

    Blue shift describes the decrease in wavelength as a source approaches an observer.

  • State the feature of the diagram that identifies that the car is stationary when sound is emitted from the horn.

    A car is in the centre of three equally spaced concentric circles. A double-headed arrow between the second and third circles indicates this is the wavelength.

    The equally spaced wavefronts on the diagram identify that the car is stationary when sound is emitted from the horn.

    A car is in the centre of three equally spaced concentric circles. A double-headed arrow between the second and third circles indicates this is the wavelength.

  • What feature of the diagram shows that the observer hears a higher pitch as the source moves towards them?

    A moving source is at the centre of four concentric circles. The circles are not evenly spaced. The circles are closer together on the right side next to the stationary observer.

    The feature of the diagram that shows that the observer hears a higher pitch as the source moves towards them is that the wavefronts are closer together next to the observer.

    A moving source is at the centre of four concentric circles. The circles are not evenly spaced. The circles are closer together on the right side next to the stationary observer.

  • Define the Doppler shift for light.

    The Doppler shift for light is the change in frequency or wavelength of light due to the relative motion of the source and observer.

  • What is the equation for Doppler shift in terms of wavelength?

    The equation for Doppler shift in terms of wavelength is fraction numerator capital delta lambda over denominator lambda end fraction ​ almost equal to space fraction numerator increment v over denominator c end fraction ​

    Where:

    • increment lambda = change in wavelength, measured in metres (m)

    • lambda = wavelength, measured in metres (m)

    • increment v = relative velocity of source and observer, measured in metres per second (m s-1)

    • c = the speed of light, measured in metres per second (m s-1)

  • True or False?

    The Doppler shift has units.

    False.

    The Doppler shift has no units because it is a ratio of two quantities with the same units (wavelength, frequency or speed).

  • How is the relative speed between the source and a stationary observer calculated?

    The relative speed between the source and a stationary observer is calculated using the equation capital delta v equals v subscript s ​ minus space v ​ subscript o

    Where:

    • v subscript s = speed of source, measured in metres per second (m s-1)

    • v subscript o = speed of observer, measured in metres per second (m s-1)

  • State the equation for Doppler shift in terms of frequency.

    The equation for Doppler shift in terms of frequency is fraction numerator capital delta f over denominator f end fraction ​ almost equal to space fraction numerator increment v over denominator c end fraction ​

    Where:

    • increment f = change in frequency, measured in metres (m)

    • f = frequency, measured in metres (m)

    • increment v = relative velocity of source and observer, measured in metres per second (m s-1)

    • c = the speed of light, measured in metres per second (m s-1)

  • What is the change in wavelength formula for Doppler shift?

    The change in wavelength formula for Doppler shift is capital delta lambda equals lambda subscript 0 ​ minus space lambda

    Where:

    • lambda subscript o = observed wavelength from the source, measured in metres (m)

    • lambda = reference (original) wavelength, measured in metres (m)

  • Which type of Doppler shift takes place when the observed wavelength of light is shorter than the actual wavelength?

    Blue shift takes place when the observed wavelength is shorter than the actual wavelength.

  • What does the symbol c represent in the Doppler shift equations?

    The symbol c represents the speed of light in the Doppler shift equations.

  • Identify the direction of motion of the light source shown in the diagram.

    Doppler effect shows redshift for lower frequency moving away and blueshift for higher frequency approaching a stationary observer.

    The direction of motion of the light source shown in the diagram is from left to right

    Doppler effect with red shift (lower frequency) and blue shift (higher frequency) as a light source moves toward the right observer, not moving relative to them.

  • Compare the expansion of the universe to dots on an expanding balloon.

    A man inflating a blue balloon with white dots. The image shows two stages: the balloon is partially inflated (left) and more inflated (right).

    The expansion of the universe compares to dots on an expanding balloon as follows:

    • As the balloon is inflated, the dots all move away from each other

    • In the same way, as the rubber stretches when the balloon is inflated, space itself is stretching out between galaxies

    • Just like the dots, the galaxies move away from each other, however, they themselves do not move

  • True or False?

    The Universe is expanding.

    True.

    The redshift observed in distant galaxies provides evidence that the Universe is expanding.

  • What does the positive velocity of a galaxy moving relative to Earth indicate?

    The positive velocity of a galaxy moving relative to Earth indicates the galaxy is moving towards the Earth.

  • What does the negative velocity of a galaxy moving relative to Earth indicate?

    The negative velocity of a galaxy indicates that the galaxy is moving away from Earth.

  • What does a greater redshift in a galaxy's observed spectrum indicate?

    A greater redshift in a galaxy's observed spectrum indicates the galaxy is moving away faster and is further from Earth.

  • How does the expansion of the Universe affect light waves?

    The expansion of the Universe affects light waves by stretching them out, shifting them towards the red end of the spectrum.

  • What is the effect of the Universe expanding on galaxies?

    The effect of the Universe expanding on galaxies is that they move away from each other.

  • How is the observed frequency for a moving sound source calculated?

    The observed frequency for a moving sound source is calculated using the equation f prime equals space f fraction numerator v ​ over denominator v plus-or-minus u subscript s end fraction

    Where:

    • f = source frequency, measured in hertz (Hz)

    • v = wave velocity, measured in metres per second (m s-1)

    • u subscript s= source velocity, measured in metres per second (m s-1)

  • What is the velocity of sound waves in the air?

    The velocity of sound waves in the air is 340 m s-1.

  • State the equation for the Doppler shift when the observer is moving towards the source.

    The equation for the Doppler shift when the observer is moving towards the source is f prime equals f fraction numerator v plus u subscript o over denominator v end fraction ​ ​

    Where:

    • f = source frequency, measured in hertz (Hz)

    • v = wave velocity, measured in metres per second (m s-1)

    • u subscript o= observer velocity, measured in metres per second (m s-1)

  • State the equation for the Doppler shift in terms of wavelength for a moving source.

    The equation for the Doppler shift in terms of wavelength for a moving source is lambda apostrophe equals lambda open parentheses 1 space plus-or-minus u subscript s over v close parentheses

    Where:

    • lambda = source wavelength, measured in metres (m)

    • v = wave velocity, measured in metres per second (m s-1)

    • u subscript s= source velocity, measured in metres per second (m s-1)

  • True or False?

    If a sound source moves away from the observer the observed frequency increases.

    False.

    If a sound source moves away from the observer the observed frequency decreases.

  • How can the speed of a galaxy moving away from Earth be calculated?

    The speed of a galaxy moving away from Earth can be calculated using the Doppler redshift equation fraction numerator capital delta f over denominator f end fraction ​ almost equal to fraction numerator v ​ over denominator c end fraction

    Where:

    • increment f = shift in frequency, measured in hertz (Hz)

    • f = reference frequency, measured in hertz (Hz)

    • v = speed of the galaxy, measured in metres per second (m s-1)

    • c = speed of light, measured in metres per second (m s-1)

  • The Doppler shift equation for a moving source in terms of wavelength is given by the equation lambda apostrophe equals lambda open parentheses 1 space plus-or-minus u subscript s over v close parentheses.

    If the source is moving towards the observer state the operation of the fraction u subscript s over v.

    If the source is moving towards the observer, negative u subscript s over v is used.

  • The Doppler shift equation for a moving source in terms of wavelength is given by the equation lambda apostrophe equals lambda open parentheses 1 space plus-or-minus u subscript s over v close parentheses.

    If the source is moving away from the observer state the operation of the fraction u subscript s over v.

    If the source is moving away from the observer, then plus u subscript s over v is used.

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