When light travels from one material to another it usually changes direction The bending of light that occurs at the borderline of two materials is called refraction Geometrical concepts: -incident ray -refracted ray -normal to the point of incidence -incident angle -refracted angle

Refraction at the air-glass boundary

Conclusion When light waves travel from a less dense (air) to a more dense medium (glass), the ray is bent towards the normal.

What happens during refraction?

glass air The speed of light depends on the material through which the light is travelling. Why is light refracted? When light enters a different material (e.g. from air into glass), the speed of light changes. This causes the light to bend or refract. The speed of light is affected by the density of the material through which it is travelling. When light enters a more dense medium (from air into glass), its speed decreases and this is why refraction occurs

Refraction  Because the frequency of the wave is determined by the source, if the wave speed slows down, its wavelength must decrease. (And vice versa) 7 Fast Medium - low refractive index like air Slow Medium - higher refractive index like glass Frequency stays the same

Refraction causes visual effects such as this ruler appearing to be bent. Effects of refraction This happens because light from the part of the ruler in the water is refracted as it travels from the water into the air. Light rays from the stone are refracted as they leave the water. The brain assumes that these rays have travelled in straight lines and is fooled into forming an image where it thinks the light rays came from. image How does refraction make this stone look closer to the surface of the water than it really is? actual location

Willebrord Snellius ( ) Dutch astronomer and mathematician Most famous for the law of refraction (Snell’s Law) Found a new method for calculating the radius of the earth as well as π 9

Index of refraction the amount of bending depends on the optical properties of the two materials --> characterized by their index of refraction: n n is a number: n=1 for vacuum, n=1.33 for water, n=2.42 for diamond, n= for different types of glass ……. when the amount of bending is bigger, the difference in n is bigger for the two materials

The laws of refraction: Snell’s laws If light travels from material 1 with index of refraction n 1 to material 2 with index of refraction n 2 the following laws determine the direction of the refracted ray: The incident ray, the normal to the incidence point and the refracted ray are all in one plane

Absolute Refractive Index (n) is a measure of how much the speed is slowed when entering a medium from a vacuum (or air) n = speed of light in a vacuum speed of light in a medium Values include: n alcohol = 1.36 n diamond = 2.41 n glass = 1.52 n water = 1.33 Which substance does light travel the fastest? Why will you never get a number less than 1? 12