Doppler effect, redshift and the Hubble constantEdexcel International A Level Physics: Mind map

Exam questions on Doppler effect, redshift and the Hubble constant

1. An ambulance sounds a siren of constant frequency 700 Hz as it drives at constant speed along a straight road towards a stationary observer standing by the roadside, passes her, and then drives away.
   Explain why the observer hears a higher frequency than 700 Hz while the ambulance is approaching her.2 marks
2. A spectral line of hydrogen has a wavelength of 656 nm when measured in a laboratory. In the light from a distant galaxy the same line is measured at a wavelength of 662 nm. Use a speed of light of 3.00 × 10⁸ m s⁻¹ and a Hubble constant H₀ of 2.3 × 10⁻¹⁸ s⁻¹.
   Calculate the distance to the galaxy in metres.2 marks
3. Two research teams use different methods to measure the Hubble constant H₀. They obtain values of 2.2 × 10⁻¹⁸ s⁻¹ and 2.4 × 10⁻¹⁸ s⁻¹. One year is 3.16 × 10⁷ s. The age of the universe can be estimated using the Hubble constant.
   Explain why 1/H₀ gives an estimate of the age of the universe, and calculate this age in years for H₀ = 2.2 × 10⁻¹⁸ s⁻¹.3 marks