اردو

Home / Practice / Lenses and optical instruments / Worksheet

Practise online

Lenses and optical instruments

Written by Dr. Hamza Farooq (Physics)

MDCAT · Physics · 6 questions

Name: ____________________   Date: ____________

  1. The total magnification of a compound microscope is:

    • A The sum of the magnifications of the two lenses
    • B Equal to that of the objective only
    • C The difference of the two
    • D The product of the magnifications of the objective and the eyepiece

  2. An object is 30 cm in front of a convex lens of focal length 15 cm. The image is:

    • A Virtual and magnified
    • B Real and magnified
    • C Real, inverted and the same size
    • D Virtual and smaller

  3. Short-sightedness (myopia) is corrected by using a:

    • A Cylindrical lens only
    • B Concave lens
    • C Plane mirror
    • D Convex lens

  4. What is the power of a lens of focal length -25 cm?

    • A +4 D
    • B -4 D
    • C +0.25 D
    • D -0.25 D

  5. A coin at the bottom of a pool appears:

    • A Larger and deeper
    • B Shallower than it is
    • C Deeper than it is
    • D At its true depth

  6. What is the speed of light in a medium of refractive index 2? (c = 3 x 10⁸ m/s)

    • A 3 x 10⁸ m/s
    • B 6 x 10⁸ m/s
    • C 1.5 x 10⁸ m/s
    • D 1 x 10⁸ m/s

Answer key

1. D, 2. C, 3. B, 4. B, 5. B, 6. C

  1. The objective forms a magnified image, which the eyepiece magnifies again, so the magnifications multiply.

  2. An object at twice the focal length gives a real, inverted image of the same size at twice the focal length.

  3. A concave lens spreads the rays so that the image falls on the retina instead of in front of it.

  4. Power = 1 / f in metres = 1 / (-0.25) = -4 dioptres.

  5. Light bends as it leaves the water, so the coin seems to be raised.

  6. v = c / n = 3 x 10⁸ / 2 = 1.5 x 10⁸ m/s.