“LIGHT WAVES”

Andrea C. Cango y Lucía A. Chalán

School of Biochemistry and Pharmacy, University Técnica Particular of Loja, Section 11-01-608, Loja, Ecuador.

(Date: May 22, 2010)

SUMMARY:

Objects that fall in water produce waves, to know this phenomenon we studied natural light waves and its

principles, like that of Huygens, which affirmed thateach point on the front of a wave is the source of the new

waves; we will see the properties of waves like diffraction which is adeviation of light thought different

mechanisms of reflection and refraction. Other properties of light waves and interference and polarization;

interference produces distinct superimposed waves, and polarization is the alignment of vibrations of

atransverse wave.It is possible to point out that the holograph is the primary example of interference.

INTRODUCTION:

Light is a form of electromagnetic radiation similar

to radiant heat, radio waves or x-ray. In

correspondence whit the wave frequency the

colors can be received by the human eye so we

have the shortest wave length in violet (40

millionths of a centimeter) and the largest (75

millionths of a centimeter).

Trough this we can say that the highest frequencies

correspond to the shortest wavelengths, including

ultraviolet radiation and ever higher frequencies

are associated whit x-rays.

The lowest frequencies, whit longer wavelengths,

are called infrared rays, and even lower

frequencies are characteristic of radio waves.

Colors visible to the human eye are grouped in the

“visible spectrum”.

Picture 1-Ligth

The distinct colors of light have in common that

they are electromagnetic radiation that displaces

whit the same velocity, approximately 300,000

kilometers per second. They differ in their

frequency of the waves depends.

LIGHT WAVES

Picture 2- Waves

In certain experiments, light it can be considered

as a transverse wave, while in the orders it’s

necessary to considered it a flow of particles called

photons, whose individual energy depends on the

frequency of the wave.

I. HUYGENS PRINCIPLE

This principle allows the explanation of wave

propagation.

Waves crest form concentric circles called wave

fronts. Each point on the front of a wave can be

considered the front of secondary waves that

extend in all directions whit a velocity of the wave

propagation.

Picture 3 - propagation of waves and fronts

Experiment:

Proceeding: in a basin whit clean water

forcefullysubmerge a ruler and then a short

distance in fronta pen; the rulers produces the

fronts of longitudinalwaves and when they collide

whit the pen theybecame circular waves because

of interference.

Picture 4 - Huygens Principle

II. DEFRACTION

Show us that light “bends” around objects.

Flexion on light that passes around an obstacle or

trough a narrow opening disperses and produces

light and dark fragments. The separated dichroics

are joined by layers of distinct materials whose

thickness is fixed in a way so the bands of

thelongitudinal wave are reflected and the other in

transmitted; this phenomenon is known as

diffraction.

An interferential filter constructed whit these

layers transmits a band longitudinal waves that are

extremely thin and reflected the rest of the

longitudes.

Picture 5– Diffraction

III. INTERFERENCE

Shows us that light, added to light can sometimes

produce darkness in certain cases.

When two or more waves of the same time, we say

that there is interference. Interference can be

constructive when to crests or two valleys meet in

a determined point and the resulting amplitude

pulse is the sum of their amplitudes; destructive

interference is produced when a valley and a crest

of equal amplitude meet.

Picture 6 – interference pattern with two sources

IV. POLARIZATION

Indicates to us that universal vibrations are

transverse.

Polarization is an alignment of vibrations of a

transverse wave, generally by the elimination of

waves of other frequencies by vibration.

Polarized light is formed by individual

photonswhose electric fields vectors are

completely aligned in the same direction. Normal

light is not polarized because the photons are

emitted coherently.

When light crosses a polarized filter, the electric

field interacts more intensely whit oriented

molecules in a determined direction. This makes

the light divide in two, whit electrical vectors (as

you can see in the illustration). A second filter

positioned 90° in respect to the first absorbs the

rest of the photons; if the angle is different, it only

absorbs a part of the light.

Picture 7– polarized plane waves

V. HOLOGRAPH

The primary example of interference is the

hologram.

Process that permits taking three dimensional

photographs by way of connected light.

The hologram is a succession of flat waves that

came in this case from the left. The light passes

through the transparent spaces of the hologram and

each space creates semispherical waves that

propagate to the right. In the imagen on the right

we have drawn the most interesting part of the

wave crest.

It is clear that the waves that go through the spaces

of the plate multiply in order to produce more

semispherical waves similar to those produce by

the reflected light from the point of the scene. An

observed situated on the right of the plate sees

light that seems to leave from a point situated in

the site that was the point of the scene. This is

what is clone to let the hologram occur - or better-

the light that has “good” phase in a “good” site.

Picture 8- hologram

CONCLUSIONS:

Through wave frequency in the visible

spectrum colors can be from the smallest

to the largest picked up.

Light can be fluid or transverse waves.

The front of a wave is considered the

origin of secondary waves in different

directions.

The properties of waves are refraction,

interference are diffraction.

BIBLIOGRAPHY:

Basic text:

Paul G. Hewit. 2007. Física Conceptual (Décima

edición, Pearson Educación). México.

Supplementary texts:

1. Eugene Hecht. 2001. Fundamentos de

Física (Segunda edición. Thomson

Learnig). México.

2. Mauricio Bautista Ballén, Bertha Cecilia

Romero Pardo, Esteban Carrillo Chica,

Sandra Genoveva Castiblanco García,

Juan Pablo Valenzuela Tovar. Física

Santillana II (Santillana). Ecuador.

3. Paul A. Tipler. 1998. Física

Preuniversitaria (Reverté, S.A) España.

4. Paul G. Hewit. 1999. Física Conceptual

(Tercera Edición. Pearson). México.

5. Sears, FrancisW., Zemansky, MarkW.,

Young, HughD. y Fredman, Roger

A.2004. FísicaUniversitaria (Undécima

edición, volume 2. Pearson). México.

6. Alan H. Cromer. 1998. Física para las

ciencias de la vida (Segunda Edición.

Reverté). México.

7. Michel Valero. 1977. FISICA Volumen 2

(Norma). Colombia.