Lesson 10.1.1

10.1.1 Intensity, luminosity and the inverse square law Quiz: Pearson Edexcel Physics, Unit 10

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 10.1.1, Intensity, luminosity and the inverse square law: 20 multiple choice questions for the Pearson Edexcel Physics (9PH0), Unit 10: Space, written with Revision Ninja.

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The 20 questions

  1. What is the SI unit of intensity?

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

  2. What physical quantity is defined as the total power radiated by a star?

    • Intensity
    • Luminosity
    • Irradiance
    • Radiant flux

  3. If distance from a point light source is doubled, how does intensity change?

    • Quarters
    • Halves
    • Eighths
    • Quadruples

  4. Which quantity is inversely proportional to the square of the distance from a source?

    • Intensity
    • Luminosity
    • Redshift
    • Wavelength

  5. A star has luminosity 3.8 x 10^26 W and is at distance 1.0 x 10^17 m. What is the intensity received?

    • 3.8 x 10^-9 W m^-2
    • 1.2 x 10^-9 W m^-2
    • 3.0 x 10^-7 W m^-2
    • 3.0 x 10^-9 W m^-2

  6. A lamp gives intensity 20 W m^-2 at distance 4.0 m. What is its luminosity?

    • about 4.0 kW
    • about 0.25 kW
    • about 16 kW
    • about 1.0 kW

  7. A source gives intensity 80 W m^-2 at 3.0 m. What is the intensity at 6.0 m?

    • 10 W m^-2
    • 160 W m^-2
    • 40 W m^-2
    • 20 W m^-2

  8. Two stars have the same intensity at Earth. Star A is twice as far away as star B. What is L_A / L_B?

    • 0.5
    • 2
    • 4
    • 8

  9. What is the intensity at Earth from the Sun, using L = 3.8 x 10^26 W and d = 1.5 x 10^11 m?

    • about 5.4 x 10^3 W m^-2
    • about 1.3 x 10^6 W m^-2
    • about 1.3 x 10^3 W m^-2
    • about 1.3 x 10^2 W m^-2

  10. A detector of area 2.0 x 10^-4 m^2 receives intensity 5.0 x 10^-9 W m^-2. What power does it receive?

    • 2.5 x 10^-12 W
    • 1.0 x 10^-12 W
    • 1.0 x 10^-9 W
    • 4.0 x 10^-13 W

  11. A star of luminosity 1.0 x 10^28 W produces intensity 1.0 x 10^-10 W m^-2 at Earth. What is its distance?

    • 2.8 x 10^14 m
    • 1.3 x 10^36 m
    • 8.0 x 10^18 m
    • 2.8 x 10^18 m

  12. Two identical lamps are placed at 3.0 m and at 9.0 m from a detector. What is the ratio of the intensity at 9.0 m to that at 3.0 m?

    • 1/27
    • 1/6
    • 1/9
    • 1/3

  13. What factor causes the stellar inverse square law to be an approximation?

    • Constant temperature
    • Interstellar absorption
    • Stellar rotation
    • Spherical geometry

  14. Star P is 4 times as luminous as star Q, and is twice as far from Earth. What is the ratio I_P / I_Q?

    • 4
    • 0.5
    • 2
    • 1

  15. Star X is 100 times more luminous than star Y. How many times further away than Y must X be to appear equally bright?

    • 50 times
    • 10 times
    • 100 times
    • 1/10 of the distance

  16. Which quantity can be calculated directly from a star's measured intensity and distance?

    • Surface temperature
    • Luminosity
    • Radius
    • Mass

  17. A star has luminosity 8.0 x 10^26 W and intensity 1.0 x 10^-9 W m^-2 at Earth. What is its distance in metres?

    • about 8.0 x 10^17 m
    • about 2.5 x 10^17 m
    • about 2.5 x 10^14 m
    • about 1.3 x 10^17 m

  18. Star A has four times the luminosity and twice the distance of Star B. Compare their intensities.

    • Star A higher
    • Equal intensities
    • Star A double
    • Star B higher

  19. Intensity is defined as radiant power transferred per unit what?

    • Time
    • Length
    • Volume
    • Area

  20. Dividing a star's luminosity by four pi times its distance squared yields which quantity?

    • Peak wavelength
    • Surface temperature
    • Intensity
    • Absolute magnitude

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