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Waves at boundaries and refraction
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When waves meet a new material they can be reflected, refracted, transmitted or absorbed.
At a boundary
Waves can be reflected (bounce back), refracted (change direction), transmitted (pass through) or absorbed (energy taken in).
Refraction
Waves change speed when they enter a new medium. If they hit the boundary at an angle, they change direction.
Light slows down entering glass and bends towards the normal. It speeds up leaving and bends away from the normal.
The normal is an imaginary line at 90° to the surface.
Light slows down entering glass and bends towards the normal. It speeds up leaving and bends away from the normal.
The normal is an imaginary line at 90° to the surface.
Reflection
angle of incidence = angle of reflection, both measured from the normal.
Light enters a glass block at an angle. Which way does it bend?
- Light slows down in glass.
- So it bends towards the normal.
Answer: Towards the normal.
Waves at a boundary can be reflected, refracted, transmitted or absorbed. Refraction is a change of direction caused by a change of speed. Angle of incidence = angle of reflection.
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