PROPERTIES of WAVES DIFFRACTION 1 Diffraction of water

PROPERTIES of WAVES DIFFRACTION 1

Diffraction of water waves The bending of waves around a barrier is called diffraction. Shadow region Water waves ”bend” around corners Diffraction Single slit diffraction 2

Diffraction through an opening: Diffraction and gaps Amount of diffraction ∝λ Amount of diffraction ∝ 1 width of the opening The narrower the opening, the greater the diffraction. 3

Christiaan Huygens A Dutch mathematician, astronomer and physicist who invented the first pendulum clock, developed mathematical relationships of circular motion and supported and developed the wave theory of light. 4

Huygens explains diffraction Wave fronts Small circular wavelets are produced by each point on the wave front Huygens explanation 5

• The small wave fronts that spread out from each point on a wave front form a new wave front on the envelope of these secondary wave fronts. • When straight wave fronts pass the edge of a boundary they continue in the forward direction. 6

• The wavelets starting at the edge of the shadow region are able to spread out into the shadow region because there are no other wave fronts to interfere destructively and cancel the sideways contribution. 7

Single slit diffraction Huygens explains diffraction Single slit diffraction of light: Broad central band flanked by alternating bright and dark stripes of constructive and destructive interference from the single slit. 8

Broad band with ‘fringes’ Viewing a vertical light source through a narrow single slit. The degree of diffraction: Broad Fringes Where w is the width of the slit. The diffraction of light clearly demonstrates the wave nature of light. Diffraction - widths & frequencies 9