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

Bending light with glass

Science · Waves, Light & Sound · ages 15-16
Name ______________________   Date ____________

  1. Light of a single frequency crosses a stationary boundary from air into water. Which quantities change?

    • Speed and wavelength
    • Frequency only
    • Speed, frequency and wavelength

  2. You view a submerged straw through the water's surface from air at a slant. Why can it look displaced from the part above water?

    • Water changes the straw's colour and physically curves its shape
    • Light from underwater bends as it speeds up into air
    • The glass enlarges every part equally and curves the whole straw

  3. A ray travels along the normal from air into ordinary glass. Its speed decreases. What happens to its direction?

    • It turns towards the normal despite already travelling along it
    • It turns away from the normal because its speed decreases
    • It continues in the same direction

  4. How does a camera focus a distant scene using its converging lens?

    • A virtual image from an object inside F lands on the sensor
    • Every scene is magnified without actual rays meeting at the sensor
    • A real, inverted image of the distant scene lands on the sensor

  5. A stamp is inside the focal length of an ideal thin converging lens. What image does an observer on the outgoing side see?

    • Real, inverted and reduced
    • Virtual, upright and magnified
    • Real, inverted and magnified

  6. Optical fibres can carry light signals using total internal reflection.

    Circle one:   True   False

  7. For a stamp inside a converging lens's focal length, outgoing rays spread apart and their backward extensions meet on the stamp's side. Why can a screen there not display this image?

    • Only extensions meet there; actual outgoing rays do not
    • Actual rays meet there but move too slowly to reach a screen
    • Actual rays meet there but the screen must be on the other side

  8. A student draws a transmitted ray entering ordinary glass from air at nonzero incidence, bending away from the normal. What corrects the drawing?

    • Its speed increases, so the away-from-normal direction is correct
    • It should bend towards the normal as its speed decreases
    • Its speed stays fixed, so the ray should continue without bending
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Answer key

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

Bending light with glass W1-mt_u8GKuBMmzC-s1

  1. Speed and wavelength · Frequency stays fixed. Speed decreases in water, and v = fλ gives a shorter wavelength.
  2. Light from underwater bends as it speeds up into air · Light from the submerged straw refracts out of water. Tracing its final direction backward shifts the apparent position.
  3. It continues in the same direction · At normal incidence, speed can change without a direction change.
  4. A real, inverted image of the distant scene lands on the sensor · The distant scene is beyond 2F. Actual rays form a real, inverted, reduced image on the sensor.
  5. Virtual, upright and magnified · Backward extensions locate an upright, magnified virtual image on the stamp's side.
  6. True · At a higher-index core to lower-index cladding boundary, rays above the critical angle reflect internally along the fibre.
  7. Only extensions meet there; actual outgoing rays do not · The apparent image location is found by backward extensions. Actual outgoing rays do not converge there to form a screen image.
  8. It should bend towards the normal as its speed decreases · Ordinary glass slows light relative to air. At nonzero incidence, the transmitted ray bends towards the normal.
Worksheet · LightMySky