Polarisation as Evidence for Transverse Waves · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.
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Polarisation shows transverse oscillation

Science · Waves, Light & Sound · ages 16-17
Name ______________________   Date ____________

  1. Two ideal polarising filters with axes 90 degrees apart transmit no light, with no material between them.

    Circle one:   True   False

  2. Which wave type can have its sideways oscillations restricted to one direction by linear polarisation?

    • Transverse waves
    • Longitudinal waves
    • Either type equally

  3. For fixed unpolarised input and two ideal polarising filters, which arrangement gives the greatest transmitted intensity?

    • Their axes meet at 45 degrees
    • Their axes are parallel
    • Their axes meet at 90 degrees

  4. Why can't ordinary longitudinal sound in air be polarised?

    • Air particles oscillate along the direction of travel
    • Air particles oscillate sideways in every possible plane
    • Air particles carry an electric field through optical filters

  5. Why can polarising sunglasses with vertical transmission axes reduce glare reflected from horizontal water?

    • They increase the horizontal electric-field component
    • They turn the reflected light into longitudinal waves
    • They reduce the horizontal electric-field component

  6. A linearly polarised radio wave reaches a straight rod aerial. With other conditions fixed, which rod alignment gives the strongest response?

    • Rod parallel to the electric field
    • Rod perpendicular to the electric field
    • Rod parallel to the wave's travel direction

  7. Unpolarised sunlight passes through one ideal polarising filter. What describes the transmitted light?

    • Light remains unpolarised because all components pass
    • Light linearly polarised along the transmission axis
    • Light linearly polarised along the direction of travel

  8. Rotating one ideal polarising filter in unpolarised light gives constant average output. A learner concludes the light is longitudinal. What explains the observation?

    • Constant output establishes longitudinal oscillations
    • Rotating one filter prevents transverse waves passing
    • Unpolarised light can give a constant reading
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Answer key

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

Polarisation shows transverse oscillation W1-mt_mCbxv77qDA-s1

  1. True · After the first filter, the electric field is perpendicular to the second filter's transmission axis, so its transmitted component is zero.
  2. Transverse waves · Linear polarisation selects a transverse oscillation direction. A longitudinal wave has no sideways direction to select.
  3. Their axes are parallel · Parallel axes let the second filter transmit all the polarised light coming from the first filter.
  4. Air particles oscillate along the direction of travel · Longitudinal sound has no transverse oscillation direction for a polarising device to select.
  5. They reduce the horizontal electric-field component · Such glare often has more horizontal electric-field oscillation. A vertical transmission axis reduces that component.
  6. Rod parallel to the electric field · The rod responds to the electric-field component along its length, which is greatest for parallel alignment.
  7. Light linearly polarised along the transmission axis · The transmitted electric field oscillates along the filter's transmission axis, perpendicular to the light's travel direction.
  8. Unpolarised light can give a constant reading · A single ideal filter gives constant average output for unpolarised light. The observation does not rule out transverse oscillations.
Worksheet · LightMySky