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Astrophysics

Doppler effect

  • 5 things to know
  • Paper 3, section B

Overview

The frequency and wavelength shift formulae, red and blue shift, and binary star spectra.

What you need to know

Answer each one before you reveal it.

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Numbers

What does Δf mean in the Doppler formula, and what is the redshift parameter z?

Numbers

What do Δλ, v and c represent in the redshift formulae?

Numbers

When are the Doppler formulae valid, and what sign does z take for a source moving towards us?

Numbers

Which radiation do the Doppler formulae apply to, how do a binary star's lines shift as it approaches, and how does the shift vary over an orbit?

Numbers

How is a quasar's recession speed found from z, what is it for z = 0.06, and what do quasar spectra reveal?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    In the Doppler effect formula Δf/f = v/c, what does Δf represent?

    Model answer

    Δf is the change in observed frequency.

  2. 2

    State the Doppler effect formula relating frequency shift to velocity.

    Model answer

    Δf/f = v/c

  3. 3

    What is the redshift parameter z?

    Model answer

    z is a dimensionless quantity defined as z = Δλ/λ = v/c, representing the fractional change in wavelength due to relative motion.

  4. 4

    In the redshift formula z = Δλ/λ, what does Δλ represent?

    Model answer

    Δλ is the change in observed wavelength compared to the emitted wavelength.

  5. 5

    In the context of redshift, what does v represent in z = v/c?

    Model answer

    v is the recessional velocity of the source relative to the observer.

  6. 6

    In the redshift formula z = v/c, what does c represent?

    Model answer

    c is the speed of light.

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