CAIE A-Level Physics 25.3.2 Redshift

Practise interpreting redshift data and using wavelength or frequency shifts to calculate relative recession speed, including the sign and size of the shift.

Exam points

use Δλ/λ ≈ Δf/f ≈ v/c to calculate recession speed or wavelength/frequency shift
interpret the sign and size of a redshift from spectral data

[Maximum number: 1]

A spectral line from a star within a galaxy is observed to have a wavelength of 660.9 nm . The same spectral line measured in the laboratory is observed to have a wavelength of 656.3 nm .

Show that the speed of the star relative to the Earth is $2.1 \times 10^{6} \mathrm{~ms}^{-1}$ .

$\frac{660.9-656.3}{656.3} \approx \frac{v}{3.0 \times 10^{8}}$ leading to $2.1 \times 10^{6} \mathrm{~m} \mathrm{~s}^{-1}$

B1

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25.3.2—Redshift of electromagnetic radiation question 1