Doppler effect, redshift and the expanding universeEdexcel A-Level Physics: Mind map

Exam questions on Doppler effect, redshift and the expanding universe

1. An ambulance travels along a straight road at a steady speed while its siren emits a constant note of frequency 700 Hz, measured by the driver. A pedestrian stands at the side of the road, and the ambulance drives past her.
   Explain why the pedestrian hears a higher frequency than 700 Hz as the ambulance approaches.2 marks
2. Astronomers study the light from a distant galaxy. The hydrogen line that has a wavelength of 656.3 nm when measured in a laboratory is observed in the galaxy's spectrum at a wavelength of 662.9 nm. Take $c = 3.00 \times 10^{8}$ m s⁻¹.
   Calculate the speed at which the galaxy is receding from the Earth.2 marks
3. A galaxy is a distance of $4.5 \times 10^{24}$ m from Earth. Take the Hubble constant as $H_0 = 2.2 \times 10^{-18}$ s⁻¹ and $c = 3.00 \times 10^{8}$ m s⁻¹. A hydrogen line that has a wavelength of 486.1 nm in the laboratory is observed in light from this galaxy.
   Calculate the speed at which this galaxy is receding from the Earth.3 marks