Physical ScienceCHAPTER 23

Waves

Waves transmit energy!!!

Mechanical Vs. ElectromagneticWaves Waves

Mechanical WavesNeed medium

(gas, liquid, solid) 

Examples: Sound, water waves

Electromagnetic WavesNo medium needed.

 Example: Visible Light

(ROYGBIV), Ultraviolet, Infrared,Microwaves, etc…

http://www.lbl.gov/MicroWorlds/ALSTool/EMSpec/EMSpec2.html

3 main characteristics of all Waves1. Amplitude (high amplitude means high energy) 2. Wavelength (Unit: meters) 3. Frequency

Units: cycles/secWaves/sec 1/sHertz (Hz)

Frequency Example Problem

1. A boy standing on a dock counts 20 waves pass by in 5 seconds. What is the frequency of the waves?

f = #waves / time

20 waves / 5 seconds = 4 Hz

Frequency Example Problem #2

2. If the frequency of the waves is increased to 8 Hz, how many waves will pass by theboy in 2 seconds?

f = #waves / time

8 Hz = #waves / 2 seconds

8 Hz x 2 seconds = 16 waves

MECHANICAL WAVES (2 TYPES)

TRANSVERSE WAVES

LONGITUDINAL WAVES

SURFACE WAVES

http://www.gmi.edu/~drussell/Demos/waves/wavemotion.html

TRANSVERSE WAVE

LONGITUDINAL WAVE

SPEED OF WAVESspeed = frequency x wavelength

v = f x λ

Example #1A wave on a lake is traveling with a velocity of 8 m/s.the frequency is 2 Hz. What is the wavelength ofthis wave?

8 m/s = 2 Hz x λ

λ = 4 m

The Type Of Medium Determinesthe Speed of The WAVE!!

Higher Density = Slower Speed of Wave

Higher Elasticity = Faster Speed of Wave

THE 4 BASIC WAVE INTERACTIONS ARE:

1.   REFLECTION2.   REFRACTION3.   DIFFRACTION

4.   INTERFERENCE

1. REFLECTIONBouncing back of waves upon

reaching another surface.

THE LAW OF REFLECTION STATES THAT THE ANGLE OF INCIDENCE IS EQUAL TO THE

ANGLE OF REFLECTION. 

2. REFRACTIONBending of waves due to a change in

speed.

3. DIFFRACTIONBending of waves around the edge

of an obstacle.

4. INTERFERENCE

1.   CONSTRUCTIVE INTERFERENCEWhen waves combine and produce a wave that is greater than either of the waves alone.

2.   DESTRUCTIVE INTERFERENCEWhen waves combine and produce a wave that is less than either wave alone.

Applet Interference by 3 wavessimultaneously.

http://www.chipr.sunysb.edu/eserc/ProjectJava/WaveInteractionApplet/

Another wave website to look at:http://www.howe.k12.ok.us/~jimaskew/pwave.htm

STANDING WAVES  RESONANT FREQUENCY (or natural frequency)The frequency at which a standing wave occurs.

RESONANCEThe ability of an object to vibrate by absorbing energy of its own natural frequency. Video clip of the Tacoma Narrows Bridge November 1940http://www.gmi.edu/~drussell/Demos.html 

NODESStationary points of a standing wave.  

ANTINODESLoops of a standing wave where maximum oscillation of the medium occurs.