Reflection and Refraction (pg 32-35)

• All electromagnetic waves are transverse.
• When light reflects from an uneven surface, the light reflects off at all different angles and you get a diffuse reflectiom.
• When light reflects from an even surface, the light reflects off at the same angle and you get a clear reflection.
• Law of reflection:

  Angle of incidence = Angle of reflection
• The angle of incidence is the angle between the incoming wave and the normal.
• The angle of reflection is the angle between the reflected wave and the normal.
• Waves travel at different speeds in substances which have different densities.
• Electromagnetic waves travel more slowly in denser media.
• Sound waves travel faster in denser substances.
• If the second material is denser than the first, the refracted ray bends towards the normal - this is because it slows down. The angle between the refracted ray and the normal is smaller than the angle of incidence.
• If the second material is less dense than the first, the angle of refraction is larger than the angle of incidence - this is because it speed up and bends away from the normal.
• Every transparent material has a refractive index.
• The refractive index of a transparent material tells you how fast light travels in that material.
• Refractive index formula:

  refractive index = speed of light in a vacuum / speed of light in that material
• Refractive index formula:

  $n=$$c/v$
• The refractive index is always a number larger than one. It has no units because it's a ratio.
• The higher the refractive index, the slower the speed of the light.
• The speed of light in air is about the same as in a vacuum, so the refractive index of air is 1.00.
• Snell's Law says that when an incident ray passes into a material:

  $n=$$sin(i) / sin(r)$
• Light going from a material with a higher refractive index to a material with a lower refractive index speeds up and so bends away from the normal.
• The critical angle is the angle of incidence that produces an angle of refraction of 90º.
• If the angle of incidence is less than the critical angle: most of the light passes out but a little bit is internally reflected.
• If the angle of incidence is equal to the critical angle: the emerging ray comes out along the surface. There's a lot of internal reflection.
• If the angle of incidence is greater than the critical angle: no light comes out. It's all internally reflected.
• Snell's law to find critical angles:

  $sinC=$$1 / n$
• The higher the refractive index, the lower the critical angle.