IB Physics HL C 5 3 Light Doppler Approximation Questions

Apply the low-speed light Doppler approximation to red-shift, blue-shift, radar speed, spectral lines and Hubble-law calculations.

Exam points

apply the low-speed light Doppler approximation to relate fractional frequency or wavelength shift to source speed and the speed of light
calculate recession or approach speed from shifted spectral lines, red-shift factor, radar frequency change and reflected-signal evidence
use red-shift and Hubble law to calculate galaxy distance or the Hubble constant and interpret the factor of two in radar reflection

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Study C.5.3—Light Doppler approximation conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

[Maximum number: 2]

Star A is a main sequence star.

The data for Star A and the Sun are given in a table.

Table for Question IB Physics HL C 5 3 Light Doppler Approximation Questions question 1 — IB Physics HL

Determine the speed, in $\mathrm{km} \mathrm{s}^{-1}$ , of Star A relative to Earth.

$\begin{aligned} v=\frac{\Delta \lambda}{\lambda} c=\frac{0.007}{100} \times 3 \times 10^{8}=21000 21 \mathrm{~km} \mathrm{~s}^{-1} \end{aligned}$

Allow ECF for MP2.

Do not award MP1 for use of the Doppler formulas for sound and mechanical waves.

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IB Physics HL C 5 3 Light Doppler Approximation Questions question 1