Lesson 5.4.2

5.4.2 Lens power and the thin lens equation Quiz: Pearson Edexcel Physics, Unit 5

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 5.4.2, Lens power and the thin lens equation: 20 multiple choice questions for the Pearson Edexcel Physics (9PH0), Unit 5: Waves and Particle Nature of Light, written with Revision Ninja.

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The 20 questions

  1. How is the power P of a thin lens defined?

    • P = f in centimetres
    • P = 1/f, with f in metres
    • P = f/1
    • P = f squared

  2. What is the SI unit of lens power?

    • The metre
    • The dioptre, equal to m^-1
    • The newton per metre
    • The watt

  3. What sign does the power of a converging lens have compared with a diverging lens?

    • Both have positive power
    • Converging lenses have positive power and diverging lenses have negative power
    • Converging lenses have negative power and diverging lenses have positive power
    • Both have negative power

  4. Two thin lenses are placed in contact with powers P1 and P2. What is the power of the combination?

    • P1 x P2
    • P1 + P2
    • 1/(P1 + P2)
    • P1 - P2

  5. Which equation is the thin lens equation, using the real-is-positive convention?

    • 1/u + 1/v = f
    • 1/u - 1/v = 1/f
    • 1/u + 1/v = 1/f
    • u + v = f

  6. Under the real-is-positive convention, what sign is given to the image distance of a virtual image?

    • Negative
    • Equal to the object distance
    • Positive
    • Zero

  7. Which expression gives the linear magnification of a thin lens?

    • m = u/v
    • m = v/u
    • m = v - u
    • m = f/u

  8. A thin converging lens has focal length 0.25 m. What is its power?

    • 0.25 D
    • 4.0 D
    • 0.40 D
    • 25 D

  9. A thin diverging lens has focal length -50 cm. What is its power?

    • 2.0 D
    • -0.50 D
    • -50 D
    • -2.0 D

  10. Two thin lenses in contact have powers +5.0 D and -2.0 D. What is the focal length of the combination?

    • 33 cm
    • 3.0 cm
    • 7.0 cm
    • 67 cm

  11. A converging lens has focal length 12 cm. An object is placed 20 cm from it. How far from the lens is the image?

    • 8.0 cm
    • 7.5 cm
    • 32 cm
    • 30 cm

  12. A thin lens forms a real image 30 cm from the lens of an object 20 cm from it. What is the linear magnification?

    • 1.5
    • 2.5
    • 0.67
    • 10

  13. A thin lens forms an image of an object 4.0 cm tall with magnification 1.5. How tall is the image?

    • 2.7 cm
    • 6.0 cm
    • 1.5 cm
    • 4.0 cm

  14. A thin lens has an object 0.60 m away and forms a real image 0.30 m from it on the other side. What is the power of the lens?

    • 3.3 D
    • 0.20 D
    • 5.0 D
    • 1.7 D

  15. A diverging lens of focal length -0.10 m has an object 0.30 m in front of it. What is the image distance?

    • -7.5 cm, a virtual image on the object side
    • +30 cm, a real image on the far side
    • +7.5 cm, a real image on the far side
    • -30 cm, a virtual image 30 cm from the lens

  16. A student says a lens of power -4 D is a converging lens, and that its focal length in metres is the reciprocal of its power. Which evaluation is correct?

    • Both parts are correct
    • The first part is wrong, because negative power means a diverging lens; the reciprocal relation is correct
    • Both parts are wrong, because powers are always positive
    • The reciprocal relation is wrong, because power equals focal length

  17. A converging lens of focal length 10 cm is placed in contact with a diverging lens of focal length -20 cm. What is the focal length of the combination?

    • -20 cm
    • 5 cm
    • 10 cm
    • 20 cm, converging

  18. A thin converging lens of focal length 0.15 m is used with an object 0.60 m away. The object is 3.0 cm tall. How tall is the image?

    • 9.0 cm
    • 1.0 cm
    • 4.5 cm
    • 0.20 cm

  19. Two thin lenses of power +4.0 D each are placed in contact. What are the power and focal length of the combination?

    • 4.0 D, focal length 25 cm
    • 8.0 D, focal length 12.5 cm
    • 8.0 D, focal length 25 cm
    • 2.0 D, focal length 50 cm

  20. Why does the real-is-positive convention give a negative image distance for a virtual image?

    • A virtual image lies on the same side of the lens as the object, the opposite side from which real image distances are measured as positive
    • Virtual images are always behind the lens, which makes their distance negative
    • A virtual image is always inverted, and inverted images have negative distances
    • The sign reverses because magnification of a virtual image is negative by definition

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