Magnifiers, Microscopes and Telescopes · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Images through optical instruments

Science · Waves, Light & Sound · ages 19-21
Name ______________________   Date ____________

  1. In the lesson's compound microscope model, what image does the objective supply to the eyepiece?

    • A real, enlarged, inverted image
    • Parallel rays straight from the object
    • A virtual image already at the near point

  2. You hold a convex lens close over a small shell, inside its focal length. What do you see?

    • An upside-down, smaller image
    • An upright, enlarged image
    • A sharp image cast on the table

  3. An unobstructed telescope's clear aperture diameter doubles. At the same wavelength, with diffraction-limited optics and other conditions comparable, which two gains follow?

    • A wider true field and an upright final image
    • A longer focal length and greater angular magnification
    • More collected light and finer resolved detail

  4. Two telescopes use converging objectives and the same 2 cm converging eyepiece, with final images at infinity. Their objective focal lengths are 40 cm and 80 cm. Which has greater angular magnification magnitude?

    • Both give 20x because their eyepieces have equal focal lengths
    • The 80 cm objective gives 40x; the 40 cm one gives 20x
    • The 40 cm objective gives 40x; the 80 cm one gives 20x

  5. An eyepiece has focal length 5 cm and gives a final image at infinity. Use D = 25 cm. What is its angular magnification?

    Answer: ______________

  6. A telescope's magnification increases while its eyepiece apparent field stays fixed. Why does its true field cover a smaller patch of sky?

    • Increasing magnification makes the objective reject more light
    • An inverted image always covers less sky than an upright image
    • The fixed apparent field spans a smaller true sky angle

  7. A microscope calculation gives a total angular magnification of -186. What does the minus sign tell you?

    • The final image is inverted
    • The image is 186 times smaller
    • The objective is faulty

  8. A microscope with a 10x objective and a 5x eyepiece magnifies 15x.

    Circle one:   True   False

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Answer key

For grown-ups. Fold this page away before handing over the rest.

Images through optical instruments W1-mt_f30rUsqYkN-s1

  1. A real, enlarged, inverted image · The specimen is just beyond the objective's focus. The objective forms a real, enlarged, inverted intermediate image that becomes the eyepiece's object.
  2. An upright, enlarged image · Inside the focal length a convex lens gives a virtual image that is upright and enlarged.
  3. More collected light and finer resolved detail · The larger aperture collects four times the light. At the same wavelength, it halves the diffraction-limited minimum angular separation, allowing finer detail.
  4. The 80 cm objective gives 40x; the 40 cm one gives 20x · Use |M| = f_obj/f_eye. The magnitudes are 40/2 = 20 and 80/2 = 40, so the telescope with the 80 cm objective magnifies more.
  5. 5 · For infinity viewing, M = D/f = 25 cm/5 cm = 5.
  6. The fixed apparent field spans a smaller true sky angle · Approximately, true field = apparent field/|M|. With apparent field fixed, increasing magnification reduces the true angle covered on the sky.
  7. The final image is inverted · The sign records orientation: the final image is inverted.
  8. False · The two magnifications multiply, so this microscope magnifies 50x.
Worksheet · LightMySky