1.To recap ray diagrams 2.To understand the concept of refraction 3.To be able to conduction refractive index calculations Book Reference : Pages

Within the optics topic it is convenient to show the passage and behaviour of light as “ray diagrams”. These should: 1.Be drawn with a pencil and ruler 2.Contain exactly 1 arrow head per ray “branch” 3.Show the normal (typically as a dotted line) at right angles to whatever it is normal to!

Refraction is the change in direction of a wave due to a change in its speed. Most commonly seen when a wave passes from one to another

The classic practical for refraction involves sending a single ray of light from air through glass blocks at different angles... Refraction2 animation Incident ray Refracted ray Emergent ray Angle of incidence (i) Angle of refraction (r)

From the classic practical we reach the following conclusions: The light ray bends towards the normal when travelling from less optically dense to more optically dense materials (e.g. air to glass) The light ray bends away from the normal when travelling from more optically dense to less optically dense materials (e.g. Glass to air) When parallel to the normal, refraction appears to not apply since the ray continues along the normal. Refraction (as in change of speed) still occurs just has no effect on the direction

Incident and emergent rays are parallel On exit from glass block, new incident ray (i 2 ) is equal to first angle of refraction r 1 Similarly for r 2 and i 1 i1i1 i2i2 r1r1 r2r2

If we calculate: Sin i Sin r For a range of angles we find that the result is a constant. We call this the refractive index of the material n = Sin i Sin r refractive index : measure of the bending of a ray of light when passing from one medium into another. (Relative to a vacuum) Snell’s Law Willibord Snell

Air Eye, Aqueous humor 1.33 Eye, Cornea 1.38 Eye, Lens 1.41 Eye, Vitreous humor 1.34 Glass, Arsenic Trisulfide 2.04 Glass, Crown (common) 1.52 Water (0° C) Water (100° C) Water (20° C) Sugar Solution 30% 1.38 Sugar Solution 80% 1.49 Honey, 21% water content Diamond Alcohol, Ethyl (grain) 1.36