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

In partnership with Revision Ninja

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.

Host it live on the board and students join with a game code on their own devices, or revise alone with Free Play. The answers are revealed in the game.

Host this setFree Play

The 20 questions

  1. What is the SI unit of intensity?

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

  2. What is the luminosity of a star?

    • The power it receives per unit area at Earth.
    • The total power it emits in all directions.
    • The apparent brightness seen from Earth.
    • The energy it emits per unit mass per second.

  3. If the distance from a point source is doubled, what happens to the intensity received?

    • It falls to one quarter of its value.
    • It halves.
    • It stays the same.
    • It falls to one eighth of its value.

  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. Why is the inverse square law for a star only an approximation for intensity?

    • It assumes the star moves at a speed close to the speed of light relative to Earth.
    • It assumes uniform emission in all directions, with negligible absorption by the medium.
    • It assumes the star's luminosity changes with its distance from the observer over time.
    • It assumes the star has the same temperature and composition as the Sun in all cases.

  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. A star's intensity is measured at Earth. Which quantity can be found from intensity together with distance?

    • Parallax angle
    • Luminosity
    • Wavelength of the star's peak
    • Redshift

  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 of star B. Star A is also twice as far away. Which statement is correct?

    • Star A is twice as bright as star B.
    • The two stars have equal intensity at Earth.
    • Star A is half as bright as star B.
    • Star A is four times as bright as star B.

  19. Which statement about intensity is correct?

    • Intensity is measured in watts and does not depend on the area it is spread over at all.
    • Intensity increases with distance from the source, because more energy reaches the observer.
    • Intensity is the total power emitted by a star in all directions, measured in watts.
    • Intensity is power per unit area, so the same source looks fainter farther away.

  20. Which quantity is found by dividing a star's luminosity by 4 π times the square of its distance?

    • Redshift
    • Parallax angle
    • Intensity received at that distance
    • Surface temperature

All Pearson Edexcel Physics quizzes