A Level Physics (A2) chapter 14: Astronomy and cosmology MCQs with answers

By Team Megalecture · Updated 4 Nov 2026

72 exam-style questions on Astronomy and cosmology, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.

72 questions · 3 topics · 10 per test

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What chapter 14 covers

Ten Astronomy and cosmology questions with answers

Try each one, then open the answer. These ten stay the same; the test draws new ones every time.

1. The radiant flux intensity of the light from a star is 4.0 × 10−9 W m−2 at a telescope. The circular mirror of the telescope has a diameter of 2.0 m and faces the star. What power from the star does the mirror collect?

  1. A
    4.0 × 10−9 W
  2. B
    8.0 × 10−9 W
  3. C
    1.3 × 10−8 W
  4. D
    5.0 × 10−8 W
Show answer

Answer: C. P = F × area = 4.0 × 10−9 × π × (1.0)2 = 1.3 × 10−8 W. Using the diameter as the radius gives 5.0 × 10−8 W.

2. A star has a luminosity of 2.4 × 1028 W, and its spectrum peaks at a wavelength of 350 nm. Using λmaxT = 2.9 × 10−3 m K and σ = 5.67 × 10−8 W m−2 K−4, estimate its radius.

  1. A
    7.1 × 1018 m
  2. B
    2.7 × 109 m
  3. C
    2.2 × 1013 m
  4. D
    9.5 × 109 m
Show answer

Answer: B. Wien: T = 2.9 × 10−3 ÷ (350 × 10−9) = 8290 K. Then r = √(L/(4πσT4)) = √(2.4 × 1028 ÷ (4π × 5.67 × 10−8 × 82904)) = 2.7 × 109 m.

3. Several sources, each of luminosity L, are placed at different distances d from a detector. A graph is plotted of radiant flux intensity F (y-axis) against 1/d2 (x-axis). The graph is a straight line through the origin. What is its gradient?

  1. A
    L
  2. B
    4πL
  3. C
    1/(4πL)
  4. D
    L/(4π)
Show answer

Answer: D. F = L/(4πd2) = (L/4π) × (1/d2), which has the form y = mx with m = L/(4π).

4. When Hubble's law v = H0d is used with SI units, what is the unit of the Hubble constant H0?

  1. A
    s−1
  2. B
    m s−1
  3. C
    s
  4. D
    m−1 s
Show answer

Answer: A. H0 = v/d has unit (m s−1) ÷ m = s−1.

5. The radiation from a star has its peak intensity at a wavelength of 480 nm. Using Wien's displacement law with λmaxT = 2.9 × 10−3 m K, estimate the surface temperature of the star.

  1. A
    6.0 × 10−6 K
  2. B
    6.0 × 103 K
  3. C
    1.4 × 10−9 K
  4. D
    1.7 × 10−4 K
Show answer

Answer: B. T = 2.9 × 10−3 ÷ (480 × 10−9) = 6.0 × 103 K. Leaving the wavelength in nanometres gives an absurdly low temperature.

6. Which two quantities does an astronomer need in order to estimate the radius of a star using Wien's displacement law and the Stefan–Boltzmann law?

  1. A
    its luminosity and the peak wavelength of its spectrum
  2. B
    its peak wavelength and the redshift of its spectral lines
  3. C
    its radiant flux intensity at the Earth and its redshift
  4. D
    its luminosity and the redshift of its spectral lines
Show answer

Answer: A. The peak wavelength gives the surface temperature (Wien). With the luminosity, the Stefan–Boltzmann law L = 4πσr2T4 can then be solved for r. Redshift gives speed, not size.

7. A Cepheid variable star at a known distance of 1.0 × 1019 m gives a radiant flux intensity of 4.0 × 10−10 W m−2 at the Earth. A Cepheid with the same period, and so the same luminosity, in a distant galaxy gives 1.0 × 10−14 W m−2. What is the distance to the galaxy?

  1. A
    2.5 × 1014 m
  2. B
    5.0 × 1016 m
  3. C
    2.0 × 1021 m
  4. D
    4.0 × 1023 m
Show answer

Answer: C. With equal L, d ∝ 1/√F: d = 1.0 × 1019 × √(4.0 × 10−10 ÷ 1.0 × 10−14) = 1.0 × 1019 × 200 = 2.0 × 1021 m. Leaving out the square root gives 4.0 × 1023 m; the fainter star must be further away, not nearer.

8. A star has a radius of 7.0 × 108 m and a surface temperature of 5800 K. What is its luminosity? (σ = 5.67 × 10−8 W m−2 K−4)

  1. A
    3.1 × 1025 W
  2. B
    4.0 × 1026 W
  3. C
    5.6 × 1017 W
  4. D
    1.2 × 1019 W
Show answer

Answer: B. L = 4πσr2T4 = 4π × 5.67 × 10−8 × (7.0 × 108)2 × 58004 = 4.0 × 1026 W. The surface area of the star is 4πr2, and the power per unit area is σT4.

9. Which pair of objects are both used by astronomers as standard candles?

  1. A
    red giant stars and white dwarf stars
  2. B
    planets and comets
  3. C
    the Sun and the Moon
  4. D
    Cepheid variable stars and type Ia supernovae
Show answer

Answer: D. Cepheid variables (luminosity linked to their period) and type Ia supernovae (nearly the same peak luminosity) are objects of known luminosity, which is what a standard candle is.

10. The spectrum of star A peaks at half the wavelength of the spectrum of star B. The luminosity of A is 4 times that of B. What is (radius of A) ÷ (radius of B)?

  1. A
    0.25
  2. B
    0.5
  3. C
    1
  4. D
    2
Show answer

Answer: B. By Wien's law, TA = 2TB. From L = 4πσr2T4, r ∝ √L/T2 = √4 ÷ 22 = 2/4 = 0.5. A is hotter and more luminous, but smaller.

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Ways to practise this chapter

Astronomy and cosmology: questions students ask

How many Astronomy and cosmology MCQs are there?

72, each with the answer and a short explanation, across 3 topics: Standard candles, Stellar radii, Hubble’s law and the Big Bang theory. Every chapter test draws ten of them, so you can take it many times.

Is the A Level Physics (A2) chapter 14 test free?

Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.

How is the chapter test marked?

The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.

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