Review redshift and Hubble’s law in Edexcel A-Level Physics through spectral-line shifts, recession speeds, galaxy distances and universe-age estimates.
The spectrum of light emitted by the star Chi Lupi provides evidence of mercury atoms in the outer layers of the star. The light emitted from the star is compared with light emitted from a mercury lamp on Earth.
One line in the spectrum of light from Chi Lupi has a wavelength of 576.933 nm . The equivalent line in a mercury spectrum produced on Earth is 576.959 nm .
A student concluded from this data that Chi Lupi is moving towards the Earth, and that the relative velocity of Chi Lupi is about 1400 m s−1.
Deduce whether the student's conclusions are correct.
Use v/c = Δλ/λ with the wavelength measured on Earth in the denominator.
v = 13500 m s^-1.
The star is moving towards Earth because the measured wavelength is less than that from the lamp spectrum.
The calculated velocity is much larger than 1400 m s^-1, so the student is not correct about the speed.