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Waves and Quantum Behaviour

Diffraction at a narrow aperture

  • 3 things to know
  • Components 01, 02 and 03

Overview

Recall questions on when spreading at a gap is greatest, water waves through wide and narrow gaps, the single-slit pattern, angular spread, and why apertures limit a telescope or camera.

What you need to know

Answer each one before you reveal it.

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Key term

Define diffraction.

Key term

Under what condition is diffraction at an aperture most pronounced?

Key term

Describe the pattern produced when laser light passes through a single narrow slit onto a screen.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Define diffraction.

    Model answer

    Diffraction is the spreading out of a wave as it passes through an aperture or round the edge of an obstacle.

  2. 2

    Under what condition is diffraction at an aperture most pronounced?

    Model answer

    Diffraction is greatest when the width of the aperture is comparable with the wavelength.

  3. 3

    What happens to a plane water wave passing through a gap much wider than its wavelength?

    Model answer

    It carries on with almost straight wavefronts, spreading noticeably only near the edges of the gap.

  4. 4

    What happens to a plane water wave passing through a gap about one wavelength wide?

    Model answer

    It emerges as almost circular wavefronts that spread into the whole region beyond the gap.

  5. 5

    Describe the pattern produced when laser light passes through a single narrow slit onto a screen.

    Model answer

    A broad bright central band appears, with much fainter bands on either side separated by dark minima.

  6. 6

    How does the width of the central diffraction maximum change as the slit is narrowed?

    Model answer

    The central maximum becomes wider, because narrowing the slit increases the angular spread of the light.

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