Refraction & Reflection

Refraction & Reflection

1. Refraction

   • Refraction is when light bends as it crosses a boundary. Refraction happens when light rays move to a more or less dense substance.
   • Any substance that light (or another wave like sound) travels through is called a medium
   • When light goes from a less dense medium to a more dense medium: light bends towards the normal
     • E.g. glass to air
   • When light goes from a more dense medium to a less dense medium: light bends away from the medium
     • E.g. air to glass
   • When you look into a glass of water with a pencil inside the pencil may appear to be bent
     • This is because of the change in direction
       • Your brain thinks the light has travelled in a straight line. You see the end of the pencil in a different place to where it actually is
         • The pencil appears bent
           • This also explains why a swimming pool looks shallower than it actually is
   • What does a lens do?
     • There are two lenses in your body
     • The lens in each of your eyes is a convex or converging lens
       • It focuses the light and enables you to see
         • The point where the rays cross is called the focus/focal point
           • The light is refracted as it goes into the lens and as it comes out

2. Reflection

   • Why do I see an image in the mirror?
     • It appears that there is someone that looks just like you
       • This image is a virtual image
         • Your brain uses the fact that light travels in straight lines to work out where the light is coming from
   • When you look in a flat, or plane mirror
     • It is the same size and shape as you are
       • It appears to be as far behind in the mirror as you are in front
         • Left and right appear swapped
   • The Law of Reflection
     • Light needs to reflect off an object in order for you to see it
       • Light reflects off a mirror in the same way a wave reflects off a barrier
     • Angle of Incidence= Angle of reflection
   • Surfaces
     • Every surface reflects at least some light
       • You can only see your reflection in a surface that reflects light in a regular way
     • Reflection from a smooth surface is called Specular Reflection
     • Reflection from a rough surface is called Diffuse Scattering
     • To form an image, the rays from each part of the object need to refect off the surface in the same way
       • If two rays that are parallel are reflected at different angles, you won't see an image

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