IB Physics HL C.5 Doppler effect Question Bank

A4. This question is about the Doppler effect.
A source emits sound of frequency 100 Hz . The speed of sound in air is $330 \mathrm{~m} \mathrm{~s}^{-1}$.
(a) Calculate the frequency measured by an observer when
(i) the observer is stationary and the source is moving towards the observer at $120 \mathrm{~m} \mathrm{~s}^{-1}$.
(ii) the source is stationary and the observer is moving towards the source at $120 \mathrm{~ms}^{-1}$.
(b) When both source and observer are stationary the wavelength is $\lambda_{0}$ and the wavespeed is $v_{0}$.

In the table below, compare the values of measured wavelength and measured wavespeed, as measured by the observer, with respect to $\lambda_{0}$ and $v_{0}$. One of the values is given for you.

E5. This question is about red-shift.
The wavelengths of radio signals from galaxy A are found to be red-shifted from the wavelengths that would be observed from sources at rest relative to Earth.
(a) The fractional change in wavelength of the radio signals from galaxy A is $9.4 \times 10^{-3}$.

Calculate, in $\mathrm{km} \mathrm{s}^{-1}$, the average velocity of galaxy A relative to Earth.
(b) A supernova was observed within galaxy A. At the peak of its emissions, the supernova had an absolute magnitude of -20 and an apparent magnitude of 13 .

Show that the distance from Earth to the supernova is about 40 Mpc .
(c) Estimate, using your answer to (a) and the result for (b), the age of the universe.

A sample of hydrogen on Earth emits a spectral line that is measured by an Earth observer to have wavelength 500 nm . The same spectral line is emitted by a galactic source that is moving away from Earth at speed of 0.1 c . What is the wavelength of the galactic spectral line that will be measured by the Earth observer?

A car horn emits sound of frequency f. While the horn is sounding, the car moves in a straight line towards a stationary observer. The speed of the car is 0.10 v where v is the speed of sound. What is the frequency of the sound of the horn heard by the observer?

An object emitting a sound of frequency 100 Hz orbits in a horizontal circle at a rate of two revolutions per second.

An observer standing a short distance away from the object is able to hear the sound. Which of the following describes the sound the observer is able to hear?

An ambulance emits a sound of frequency f as it travels along a straight road between stationary observers A and B .

Which of the following shows how the frequency of the sound heard by each observer compares with f ?

A source emits sound of wavelength $\lambda_{0}$ and wave speed $v_{0}$. A stationary observer hears the sound as the source moves away. What are the wavelength of the sound and the wave speed of the sound as measured by the stationary observer?

A source of sound moves away from an observer. The observed frequency of the sound differs from the frequency emitted by the source because the

Two loudspeakers A and B are initially equidistant from a microphone M. The frequency and intensity emitted by A and B are the same. A and B emit sound in phase. A is fixed in position.

B is moved slowly away from M along the line MP. The graph shows the variation with distance travelled by B of the received intensity at M .