7. REFLECTION of waves and a scientific wave model

• Waves are readily reflected off smooth flat surfaces e.g. light reflected off a mirror.

  • Reflection of waves at a smooth surface (e.g. light)

  • The vertical dotted line is called the 'normal', it isn't a ray, but helps in the construction and interpretation of ray diagrams. A plane mirror means one of a perfectly flat surface.

  • Angle 2 = angle of incidence of the incident ray.

  • Angle 3 = angle of reflection of the reflected ray.

  • Angle 2 = Angle 3 - the simple 'law of reflection'

  • Angle 1 = angle 4.

  • All angles are measured with respect to the 'normal' which is at 90^o to the surface - the dotted line.

  • the 'normal' is an imaginary line at 90^o to a surface or a boundary between two media (see refraction below) at a point where the waves are hitting. It is useful when constructing ray diagrams (like the one above) to show the paths of the ways and their angles relative to the surface or boundary.

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  • The scientific wave model of reflection.

  • Think of the wavefronts as the crests of the waves e.g. as you observe ripples on water or waves at the seaside.

  • When the waves meet the flat smooth surface they are 'bounced' off symmetrically at the same angle with respect to the normal - see the first reflection diagram.

  • You can readily see this with ripple tank experiment waves - just put a barrier in their way at 45^o to their direction and the wave direction is changed by 90^o.

  • Similarly you will see the same with light ray experiments using ray box.