Lesson 9.3.1

9.3.1 Black body radiators, Stefan-Boltzmann and Wien's laws Quiz: Pearson Edexcel Physics, Unit 9

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 9.3.1, Black body radiators, Stefan-Boltzmann and Wien's laws: 20 multiple choice questions for the Pearson Edexcel Physics (9PH0), Unit 9: Thermodynamics, written with Revision Ninja.

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The 20 questions

  1. What is the defining property of a perfect black body radiator?

    • Absorbs visible light
    • Absorbs all radiation
    • Transmits all radiation
    • Reflects all radiation

  2. Which expression is the Stefan-Boltzmann law for the total power radiated by a black body?

    • L = σ T^4 / A
    • L = σ A T^4
    • L = σ A T
    • L = σ A T^2

  3. What are the SI units of the Stefan-Boltzmann constant σ?

    • J m^-3 K^-4
    • W m^-2 K^4
    • W m^-2 K^-4
    • W m^2 K^-4

  4. According to Wien's law, what happens to peak wavelength as black body temperature increases?

    • It doubles
    • It stays constant
    • It increases
    • It decreases

  5. A star's spectrum peaks at a wavelength of 500 nm. Using Wien's law, what is its approximate surface temperature?

    • about 2900 K
    • about 5800 K
    • about 11600 K
    • about 580 K

  6. A black body has surface area 0.50 m^2 and temperature 1000 K. Taking σ = 5.67 x 10^-8 W m^-2 K^-4, what is its total power output?

    • about 28 kW
    • about 283 kW
    • about 2.8 kW
    • about 5.7 kW

  7. If the absolute temperature of a black body doubles, by what factor does the power emitted per unit area increase?

    • 2
    • 8
    • 16
    • 4

  8. What is the peak wavelength of a black body at 3000 K?

    • about 0.97 micrometres
    • about 0.97 nanometres
    • about 0.097 micrometres
    • about 9.7 micrometres

  9. A black body has its peak wavelength at 1.2 micrometres. What is its temperature?

    • about 2400 K
    • about 1200 K
    • about 3500 K
    • about 4800 K

  10. A Sun-like star has radius 7.0 x 10^8 m and surface temperature 5800 K, and is treated as a black body with σ = 5.67 x 10^-8 W m^-2 K^-4. Approximately what is its luminosity?

    • about 7.9 x 10^26 W
    • about 1.2 x 10^26 W
    • about 3.9 x 10^26 W
    • about 3.9 x 10^22 W

  11. Star B has the same surface temperature as star A but twice the radius. What is L_B / L_A?

    • 4
    • 16
    • 8
    • 2

  12. A star's peak wavelength falls from 900 nm to 600 nm. What is the ratio of its final to initial absolute temperature?

    • 1.5
    • 0.44
    • 0.67
    • 2.25

  13. A black body's absolute temperature doubles while its surface area halves. Its power output was P before. What is it now?

    • 8P
    • 4P
    • 16P
    • 32P

  14. What surface property causes a real object to emit less thermal radiation than a black body?

    • Zero absorbance
    • Emissivity under 1
    • High reflectivity
    • Low thermal conductivity

  15. As a black body becomes hotter, what happens to its total emitted power per unit area?

    • It increases
    • It halves
    • It decreases
    • It stays constant

  16. Two stars have equal radii, but Star X is hotter than Star Y. Which star has greater luminosity?

    • Star X
    • Both equal
    • Neither star
    • Star Y

  17. As temperature increases, to what region of frequency does the peak of black body radiation shift?

    • Zero frequency
    • Lower frequency
    • Higher frequency
    • Same frequency

  18. Two stars have equal luminosity. Which star has the larger radius?

    • The cooler star
    • The denser star
    • The brighter star
    • The hotter star

  19. What prevents real stars from behaving as perfect black body radiators?

    • Atmospheric absorption
    • Nuclear fusion
    • Gravitational redshift
    • Rotational speed

  20. A sphere of radius 0.10 m is at 400 K and is treated as a black body. What power does it emit? Use σ = 5.67 x 10^-8 W m^-2 K^-4.

    • about 180 W
    • about 45 W
    • about 1800 W
    • about 18 W

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