Topic: Waves

Aim: How do waves behave?

Do Now: Take out last night’s HW.

HW: Ditto – Forms of Energy (in your Energy Notes packet)

Energy Castle Learning due tomorrow!!!

A

Identify each part of a wave labeled in the diagram above.

B

C

D

1. Which wave has the greatest amplitude?

2. Which wave has the greater wavelength?

3. Which wave has the greater frequency?

Whathappens if a wavehits abarrier?

1. Energy may be absorbed.2. It can bounce off.3. It can pass through it.

How do waves behave?

Reflection•Bouncing of a wave

http://www.shokabo.co.jp/sp_e/optical/labo/refref/refl1.gif

•Examples: 1. Mirror (light reflecting off the mirror)

2. Echoes = sound reflecting

http://videos.howstuffworks.com/discovery/30016-assignment-discovery-reflection-and-refraction-video.htm

Refraction•Bending of wave as it moves from 1 medium to another

•Why? Bc it changes speed

•Slows down bends toward normal–Less dense (air) more dense (water)

AIR

WATER(more dense)

(less dense)

Normal

Bends toward normal

•Speeds up bends away from normal–More dense (water) less dense (air)

GLASS

AIR(less dense)

(more dense)

Normal

Bends away from normal

Have you ever noticed that objects underwater seem closer to the surface than they really are? The light waves reflected from the swimmer’s foot are refracted away from the normal and enter your eyes.

http://videos.howstuffworks.com/discovery/29408-assignment-discovery-refraction-basics-video.htm

Let’s summarize…

1.Describe how waves can behave.

2.Explain the difference between reflection and refraction.

3.Explain why refraction occurs.

Diffraction •Bending of waves:–around object OR through a narrow opening

Water waves are being diffracted at a breakwater.

Sound waves can bend and undergo diffraction.

AM radio waves have longer wavelengths than FM radio waves do. Because of their longer wavelengths, AM radio waves diffract around obstacles like buildings and mountains. As a result, AM radio reception is often better than FM reception around tall buildings and natural barriers such as hills.

Interference •When waves overlap & combine

•2 types:1. Constructive interference =

–Waves add together (in phase)

–New amplitude = sum of all amps

When waves combine by constructive interference, the combined wave has a larger

amplitude.

2. Destructive interference = –Waves subtract from each other (out of phase)

–New amplitude = difference of amp (subtract)

–Transverse wave: Crest meets trough

–Compressional wave: Compression overlaps with rarefaction

–Ex: Sound waves that undergo DI cause loudness to decrease

When two waves with the same amplitude combine by destructive

interference, they may cancel each other out.