The Behavior of Waves

Section 11.3

South Carolina Standards• PS – 7.6

•Summarize reflection and interference of both sound and light waves and the refraction and diffraction of light waves.

Reflection

• Reflection – when a wave strikes an object and bounces off of it• All types of waves can be reflected

Law of Reflection• The wave which strikes a surface is called the

incident ray• The wave that bounces off of the surface is

called the reflected ray

Law of Reflection – the angle of incidence is always equal to the angle of reflection

Refraction

• Refraction – the bending of waves caused by a change in its speed as it moves from one medium to another• The greater the change

in its speed, the more the wave bends

Light slows down – bends towards the normal

Light speeds up – bends away from the normal

1.) Light waves enter into prism and slow down.

2.) This causes the waves to bend

3.) The different colors of light bend different amounts so the colors are separated

Concave Lens• Students should be able to draw the

resulting rays as light passes through a concave lens.Concave lenses

are known as diverging lenses because light rays are caused to spread apart as they enter and then leave the lens from the other side.

Convex Lens• Students should be able to draw the

resulting rays as light passes through a convex lens.Convex lenses

are known as converging lenses because light rays are caused to come together as they enter and then leave the lens from the other side.

Diffraction

• Diffraction – when an object causes a wave to change direction and bend around it

Diffraction and Wavelength• Amount of diffraction depends on the size of

the object the waves hit and the wavelength of the waves• If the object is smaller than the

wavelength the waves will bend around it• So sound waves which are larger will diffract much better than light waves which are much smaller

Absorption

• Waves can also be absorbed when they strike an object.• Energy is converted into thermal energy /

chemical energy• This is why wearing dark clothes in the winter

months keeps you warmer

Interference

• Interference – when two or more waves combine to form a new wave

Constructive Interference• Constructive interference – when two or

more waves add together• In transverse waves the crests will line up

with one another• In compressional waves the compressions

will line up with one another• The overall effect is to increase the

amplitude (energy) of the wave

Destructive Interference

• Destructive interference – waves subtract from one another when they overlap