A MECHANICAL WAVE IS A DISTURBANCE IN A MEDIUM.

AN ELECTROMAGNETIC WAVE DOES NOT NEED A MEDIUM FOR PROPAGATION.

THERE ARE TWO PATTERNS OF WAVE PROPAGATION.
1. LONGITUDINAL WAVES-- MOTION IN THE MATTER CARRYING THE WAVE IS ON THE SAME LINE AS THE WAVE MOVES.

2. TRANSVERSE WAVES-- MOTION IN THE MATTER CARRYING THE WAVE IS PERPENDICULAR TO THE LINE CARRYING THE WAVE.

A pulse is a wave of short duration. A periodic wave occurs again and again. Huygens Principle states how waves are propagated (transmitted) .

THE WAVE EQUATION--

A wave cycle consists of a crest (high point) and a trough (low point).
The distance from crest to crest or trough to trough is called the WAVELENGTH and denoted by the Greek letter lambda.

The time for one wave cycle is the PERIOD of the wave. The number of cyles per second is the FREQUENCY .


Waves have the following properties.

1. DIFFRACTION-- Waves bend around edges. When waves pass through an opening, they bend around both edges of the opening.

2. REFRACTION-- When waves pass from one medium to another the velocity changes and bends the wave front.This change in speed causes the effect known as refraction.

 

 

 

 

 



3. INTERFERENCE--

When a crest passes through the same place at the same time that a trough passes through then DESTRUCTIVE interference occurs and all wave motion is canceled at that one instant. When a crest passes through the same place at the same time that another crest passes through then CONSTRUCTIVE interference occurs. This also happens when two troughs occupy the same place at the same time. This produces a wave that has a very large amplitude with very high crests and very deep troughs. The amplitude is increased by the algebraic sum of the two crests and the algebraic sum of the two troughs. See below

Created by Liz Woolard

A WAVE REFLECTS FROM A MORE DENSE MATERIAL INVERTED OR UPSIDE DOWN

A WAVE REFLECTS FROM A LESS DENSE MATERIAL OR MEDIUM RIGHT SIDE UP.

4.   POLARIZATION -- 
Only transverse waves can be polarized.  Polarization occurs when a physical medium allows wave vibration in only one plane .  Electomagnetic waves--light- vibrate in an electric field and magnetic field direction at the same time and perpendicular to each other.  After entering the polarizing filter, light vibrates in only one plane.