Edexcel IGCSE Physics 8.16P Red-shift equation

Practise calculating galaxy speed, wavelength change and observed wavelength using red-shift data, graphs and unit checks.

Exam points

substitute Δλ, λ and c into the red-shift equation to calculate galaxy velocity
calculate observed wavelength by adding the wavelength change to the reference wavelength
read Δλ from a graph or spectrum before rearranging the red-shift equation

[Maximum number: 3]

Between 1929 and 1931, physicists Hubble and Humason investigated the red-shift of light from galaxies at different distances from the Earth.

The distance unit they used is the megaparsec (Mpc).

The graph shows some of the results of their investigation.

Figure for Question 8.16P Red-shift equation question 1 — Edexcel IGCSE Physics

The reference wavelength of the light used in this investigation is 660 nm.
Use information from the graph to determine the velocity of a galaxy at a distance of 0.75 Mpc.

[speed of light = 300000 km/s]

velocity = ............ km/s

Marking points:
- change in wavelength $=0.03\ \mathrm{nm}$
- substitution or rearrangement
- evaluation

Example:
$\Delta\lambda=0.03\ \mathrm{nm}$ $\frac{0.03}{660}=\frac{v}{300000}$ $v=14\ \mathrm{km\,s^{-1}}$

Accept:
- ECF from 8(b)(ii), correct within $\frac12$ small square
- ECF from incorrect reading of $\Delta\lambda$ if clear from working
- $13.6\ldots\ \mathrm{km\,s^{-1}}$

Marking guidance:
- deduct 1 mark for power-of-ten error
- award change in wavelength if seen anywhere in working

All question bank results loaded

8.16P Red-shift equation question 1