Wave properties

Wavefront – a line joining points that are in phase

- the lines you see when ripples spread on water are wavefrontsRays – arrows drawn to show the direction of wave motion

Reflection

- The bouncing of waves off a surface

Regular reflection – reflection from a smooth surface

- an image would appear to be coming from behind the surface

Diffuse reflection – reflection from a non-smooth surface

- light bounces off the surface but no image can be seen

When light hits a surface, part of the wave is reflected, part is absorbed by the atoms of the material.

When light hits a transparent material, some is transmitted through the window.

Law of reflectionThe angle of incidence equals the angle of reflection

All angles are measured to the normal line (perpendicular to the surface)

Refraction

When a wave passes from one medium into another, its velocity changes. If the wave hits the boundary at an angle, the wave also changes direction.

Index of refraction (n)- a number that relates the optical density of a substance (how fast light travels through it)

c = 3 x 108 m/sv = speed of light in substance n

Ex: What is the speed of light in water (n = 1.33)?

v = 2.26 x 108 m/s

Light travels at 2 x 108 m/s in a substance. What is its index of refraction?

The index of refraction of a liquid is 0.80. How fast does light travel in it?

Snell’s Law

= =

A water wave travelling at 20 m/s enters a shallow region where its velocity is 15 m/s. If the angle of incidence of the water wave is 50o, what is the angle of refraction?

35.2o

Light travelling through air is incident on the surface of a pool of water at an angle of 40o. Calculate the angle of refraction.