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Waves · Chapter 6: Diffraction

Year 11 Science · About 13 minutes with activities · Turn your sound on

Chapter 6 · Diffraction
Farmhouse
AM radiocomes through clearly
FM radiojust static
Through a gap
Around a barrier
Same wavelength before and after
Open seastraight wavefronts
Gap in the breakwater
Boat in the corner still rocks
Wide gap (gap ≫ λ)little diffraction
Gap ≈ λmost diffraction (180°)
Same λ before and after
Gap much wider than λ
Gap ≈ λ
Edge of a barrier
AM: wavelength hundreds of metresdiffracts around the hill
FM: wavelength about 3 mdiffracts very little
Black spot
Friend talking
Youround the corner
Sound: λ about 1 mdiffracts through the door
Light: λ tinygoes straight

Chapter 6 recap

  • Diffraction is the bending of a wave as it passes through a gap or around a barrier. The wavelength stays the same.
  • Diffraction is greatest when the gap ≈ wavelength (semicircles, about 180°). A gap much wider than the wavelength gives little diffraction.
  • Long-wavelength radio (AM) bends around hills; short-wavelength signals (FM, mobile) are blocked, leaving black spots. Sound bends round corners; light hardly does.
  • You've finished the Waves course. Revise any chapter from the home page.

Why does AM radio work behind a hill when FM drops out?

Chapter 6 · About 13 minutes · sound on

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