1. Refractive Index To be able to use Snell’s law to work out the refractive index of a material.

2. Refraction Copy and label the following diagram i = angle of incidence r = angle of refraction From less dense medium to more dense medium is always towards normal

3. Snell’s law For a light ray travelling into glass from air you should find that The angle of refraction is always less than the angle of incidence The greater the angle of incidence, i, the greater the angle of refraction, r. Snell’s law states that sin i always has the same value. sin r Prove it!

4. Refractive Index The ratio sin i is called the refractive index of the substance. sin r sin i The refractive index of the substance, n = ------- sin r This can be re-arranged to calculate the angle of incidence or refraction if you are given the refractive index of a substance. This applies when the light ray is going from air into a transparent substance of greater density, e.g. air into glass e.g. A light ray travels from air into glass across a straight boundary. The angle of incidence of the ray in the air is 32°. The refractive index of the glass is 1.55. Calculate the angle of refraction of the light ray in the glass.

5. Going the other way When a light ray travels from a transparent substance into air at a non-zero angle of incidence; The light ray is refracted away from the normal The larger the angle of incidence the larger the angle of refraction. The law of refraction can be adapted to cover both situations by using the formula: The sine of the angle in air = n x the sine of the angle in glass e.g. A light ray travels from glass to air across a straight boundary. The angle of incidence of the light ray in the glass is 40°. The refractive index of the glass is 1.55. Calculate the angle of refraction of the light in the air.

6. Summary Complete the following paragraph: moreless When a light ray travels from air to glass, the angle of refraction is always _____ than the angle of incidence. When a light ray travels from water into air, the angle of incidence in the water is ______than the angle of refraction in air. When a light ray travelling from air into glass is refracted, reducing the angle of incidence makes the angle of refraction ______.

7. Refraction sheet

8. LENSES

9. Converging (convex) lens

10. Diverging ( concave ) lens