Wave Behavior

Reflection: Waves bounce off a surface such as a mirror or wall.

• The law of reflection says that the angle of incidence is equal to the angle of reflection.

Waves may reflect from curved or plane surfaces

Refraction

• Waves bend due to a change in speed when entering another medium.

Light crossing a boundary between two mediums can slow down or speed up. It can bend toward or away from the normal .

The normal is an imaginary lin perpendicular to the boundary.

Light Travelling through a prism

• White light enters the prism on one side.• As different wavelengths of light travel through the prism, they

bend differently.• As they exit, the different wavelengths of light are seen as colors.

Diffraction: waves change shape when they encounter a barrier

Breakers may be built to keep waves from pounding the shore.

Diffraction grating consists of many tiny parallel lines

Other objects with parallel lines such as a CD cause diffraction.

What happens to a wave when….

…it runs into another wave?The two waves will pass right through each

other in an interference patternDuring the time of intersection, the size of the

resulting wave is determined by SUPERPOSITION-

Adding the displacements from equilibrium together.

Interference

When waves add together, constructive interference occurs.

When waves cancel out, destructive interference occurs.

In Phase/ Out of Phase

• In phase - Waves with crests and troughs arriving at the same time so that they reinforce each other (constructive interference)

• Out of phase – wave interference where the trough cancels out some or all of the crest of another wave

Doppler Effect – change in frequency due to the motion of a source or the observer

• A red shift refers to longer wavelengths present when objects move away from the observer

Applications of the Doppler Shift

• Ultra sound uses harmless high-frequency sound waves to produce an image so we can “see” what’s in our bodies

• Why would this be more desirable than X-rays?

Weather reporters, police officers, astronomers, and coaches all use the

Doppler effect

Caused by constructive interference

Standing Waves

Nodes and Antinodes• In a standing wave,

there are points that remain stationary

• NO MOTION. • NODES

• The bulges that show the greatest AMPLITUDE

• Are called ANTINODES

Beats• A “beat frequency” is produced

when two objects are vibrating at nearly the same frequency.

• Used for tuning orchestral instruments

Beat frequency = f1 – f2

Resonance- the tendency of an object to vibrate with a greater amplitude at certain

frequencies• One simple example is pushing a child on a

swing.• If two objects are vibrating with the same

frequency, they are said to be in “resonance”• Examples: two tuning forks- if they are “in

resonance”, the vibration of one will produce vibration in the other even if they are not touching.

Resonators• All musical instruments create standing wave

forms within them.• Wind instruments: waves of air molecules

inside the cavities• Stringed instruments have vibrating strings,

but the majority of sound is produced when that vibration is spread to a resonating box, often called the “sound board” or “sound box”

Transverse waves along a string- example: a guitar string

Watch this resonance!

• http://www.youtube.com/watch?v=zpUL6sZs6J4