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WAVE THEORY

Group 2:

Buensuceso, Elagio, Emman, Gines, Diokno

Contents

Huygens’ Wave Theory

Thomas Young’s Double Slit Experiment

EM Wave Thoery

Hertz’s Experiment on EM Waves

Huygens’ Wave Theory

Huygens’ Wave Theory

In the late 1600s, many
particles, or waves ?

Sir Isaac Newton, a
famed scientist,
supported the theory
of tiny particles,
maintaining the stance
of previous scientists.

Light

However, we know that light is part of
the

electromagnetic spectrum, the spectrum is
the collection of all waves, which
include

visible light, Microwaves, radio waves (
AM, FM, SW ), X
-
Rays, and Gamma Rays.

This was proven eventually in 1678, by a Dutch
Scientist named Christiaan Huygens.

Christiaan Huygen

Christiaan Huygens,
believed that light was
vibrating up and down
perpendicular to the
direction of

the light
travels (transverse
waves), and therefore
formulated a way of
visualizing wave
propagation.

This became known as
'Huygens' Principle'
.

Huygens’ Wave Theory

Huygens’ theory was
the successful theory
of light

wave motion
in three dimensions.

It also suggested that
light wave peaks form
surfaces like the
layers of an onion.

Wave Theory

In a vacuum, or other
mediums, the light waves
are spherical, and these
travel at the speed of
light.

This theory explains why
light shining through a pin
hole or slit will spread out
rather than going in a
straight line.

Newton vs Huygens

Some of the experiments
conducted on light theory,
both the wave and particle,
results: as Newton could
not explain the
phenomenon of light
interference, this forced
Newton's particle theory in
favor of the wave theory.

However, it was eventually
realized that matter and
waves exhibited properties
of the other.

This was due to the
unexplained
phenomenon of light
Polarization
-

scientists
were familiar with the
fact that wave motion
was parallel to the
direction of wave travel,
NOT perpendicular to
the to the direction of
wave travel, as light
does.

Huygens’ Principle

He

also

found

that

a

surface

containing

many

separate

wave

sources

appeared

as

a

single

wave

front

with

the

shape

of

the

surface
.

This

wave

front

is

termed

a

'Huygens

combination'

of

the

separate

waves
.

This

explains

how

matter's

spherical

In
-
waves

are

formed
.

The

Out
-
waves

of

others

combine

to

form

a

Huygens

'combination

wave

front'

which

forms

the

spherical

In
-
wave

of

our

wave
-
centers
.

Christian Huygens proposed a hypothesis for the geometrical
construction of the position of a common wavefront at any instant
during the propagations of waves in a medium. The postulates are:

Every point on the given wavefront called
primary wavefront*

acts as a
fresh source of new disturbance, called
secondary wavelets**

that travel
in all directions with the velocity of light in the medium.

A surface touching these secondary wavelets tangentially in the forward
direction at any instant gives a new wavefront at that instant. This is the
secondary wave front.

*
-

The envelope of all wavelets in the same phase
-

having received light from sources in the
same phase at the same time is called a wave front.

**
-

All points lying on small curved surfaces, that receive light at the same time from the same
source (primary or secondary) are called wavelets.

Thomas Young’s Double
Slit Experiment

The
double
-
slit experiment

in quantum mechanics is an experiment
that demonstrates the inseparability of the wave and particle natures
of light and other quantum particles. A coherent light source
illuminates a thin plate with two parallel slits cut in it, and the light
passing through the slits strikes a screen behind them. The wave
nature of light causes the light waves passing through both slits to
interfere, creating an interference pattern of bright and dark bands
on the screen. However, at the screen, the light is always found to
be absorbed as discrete particles, called photons.

If the light travels from the source to the screen as particles, then the
number that strikes any particular point on the screen should be
equal to the sum of those that go through the left slit and those that
go through the right slit. In other words, the brightness at any point
should be the sum of the brightness when the right slit is blocked
and the brightness when the left slit is blocked. However, it is found
that
blocking one slit makes some points on the screen brighter and
other points darker
. This can only be explained by the alternately
additive and subtractive interference of waves, not the exclusively

Although the double
-
slit experiment is now often referred to in the
context of quantum mechanics, it is generally thought to have been
first performed by the English scientist Thomas Young in the year
1801 in an attempt to resolve the question of whether light was
composed of particles (Newton's "corpuscular" theory), or rather
consisted of waves traveling through some ether, just as sound
waves travel in air. The interference patterns observed in the
experiment seemed to discredit the corpuscular theory, and the
wave theory of light remained well accepted until the early 20th
century, when evidence began to accumulate which seemed instead
to confirm the particle theory of light.

It was shown experimentally in 1972 that in a Young slit system
where only one slit was open at any time, interference was
nonetheless observed provided the path difference was such that
the detected photon could have come from either slit. The
experimental conditions were such that the photon density in the
system was much less than unity.

A

Young

double

slit

experiment

was

not

performed

with

anything

other

than

light

until

1961
,

when

Claus

Jönsson

of

the

University

of

Tubingen

performed

it

with

electrons,

and

not

until

1974

in

the

form

of

"one

electron

at

a

time",

in

a

laboratory

at

the

University

of

Milan,

by

researchers

led

by

Pier

Giorgio

Merli,

of

LAMEL
-
CNR

Bologna
.

The

results

of

the

1974

experiment

were

published

and

even

into

a

short

film,

but

did

not

wide

attention
.

The

experiment

was

repeated

in

1989

by

Tonomura

et

al

at

Hitachi

in

Japan
.

Their

equipment

was

better,

reflecting

15

years

of

in

electronics

and

a

dedicated

development

effort

by

the

Hitachi

team
.

Their

methodology

was

more

precise

and

elegant,

and

their

results

agreed

with

the

results

of

Merli's

team
.

Although

Tonomura

asserted

that

the

Italian

experiment

not

detected

electrons

one

at

a

time

a

key

to

demonstrating

the

wave
-
particle

single

electron

detection

is

clearly

visible

in

the

photos

and

film

taken

by

Merli

and

his

group
.

EM Wave Theory

Electromagnetic waves

It

consists

of

electric

and

magnetic

field

components

which

oscillate

in

phase

perpendicular

to

each

other

and

perpendicular

to

the

direction

of

energy

propagation
.

EM wave theory

The

theory

of

electromagnetic

waves

was

first

postulated

by

James

Clerk

Maxwell

and

was

confirmed

by

Heinrich

Hertz
.

Maxwell

derived

a

wave

form

of

the

electric

and

magnetic

equations,

revealing

the

wave
-
like

nature

of

electric

and

magnetic

fields,

and

their

symmetry
.

Maxwell

proved

that

light

therefore

is

an

electromagnetic

wave

through

his

equations
.

EM wave theory

A

spatially
-
varying

electric

field

generates

a

time
-
varying

magnetic

field

and

vice

versa
.

Neither

can

exist

by

themselves
.

Therefore,

as

an

oscillating

electric

field

generates

an

oscillating

magnetic

field,

the

magnetic

field

in

turn

generates

an

oscillating

electric

field,

and

so

on
.

These

oscillating

fields

together

form

an

electromagnetic

wave
.

Electromagnetism

Electromagnetic waves are a form of traveling electric and magnetic transverse
waves

A charged (positive/negative) particle can create an electric field around it. The force
of an electric field acts to electric charges just like how a gravitational field would act
to masses.

When the charge start to oscillate, back and forth, the oscillation of the electric field
will create a magnetic field that is at right angles to the electric field

The oscillation of the magnetic field would create another electric field and continue to
create each other in the process. Unlike a STATIC field, a wave cannot exist unless it
is moving. Once created, an electromagnetic wave will continue on forever unless it is
absorbed by matter.

Hertz’s Experiment on EM
Waves

In

1887
,

Hertz

designed

a

brilliant

set

of

experiments

that

tested

Maxwell's

hypothesis
.

He

used

an

oscillator

of

polished

brass

knobs,

each

connected

to

an

induction

coil

and

separated

by

a

tiny

gap

over

which

sparks

could

leap
.

Hertz

reasoned

that,

if

Maxwell's

predictions

were

correct,

electromagnetic

waves

would

be

transmitted

during

each

series

of

sparks
.

To

confirm

this,

Hertz

a

simple

of

looped

wire
.

At

the

ends

of

the

loop

were

small

knobs

separated

by

a

tiny

gap
.

The

was

placed

several

yards

from

the

oscillator
.

According

to

theory,

if

electromagnetic

waves

were

from

the

oscillator

sparks,

they

would

induce

a

current

in

the

loop

that

would

send

sparks

across

the

gap
.

This

occurred

when

Hertz

turned

on

the

oscillator,

producing

the

first

transmission

and

reception

of

electromagnetic

waves
.

Hertz

also

noted

that

electrical

conductors

reflect

the

waves

and

that

they

can

be

focused

by

concave

reflectors
.

He

found

that

nonconductors

allow

most

of

the

waves

to

pass

through
.

Another

of

his

discoveries

was

the

photoelectric

effect
.

Earlier

in

1886
,

Hertz

developed

the

Hertz

antenna

.

This

is

a

set

of

terminals

that

is

not

electrically

grounded

for

its

operation
.

He

also

developed

a

transmitting

type

of

dipole

antenna
,

which

was

a

center
-
fed

driven

element

for

transmitting

UHF

waves
.

These

antennas

are

the

simplest

practical

antennas

from

a

theoretical

point

of

view
.

Hertz

observations

of

the

photoelectric

effect

and

of

the

production

and

reception

of

electromagnetic

(EM)

waves

using

an

apparatus
.

His

consisted

of

a

coil

with

a

spark

gap,

whereupon

a

spark

would

be

seen

upon

detection

of

EM

waves
.

He

placed

it

in

a

darkened

box

to

see

the

spark

better
.

He

observed

that

the

maximum

spark

length

was

reduced

when

in

the

box
.

A

glass

panel

placed

between

the

source

of

EM

waves

and

the

absorbed

ultraviolet

that

assisted

the

electrons

in

jumping

across

the

gap
.

When

removed,

the

spark

length

would

increase
.

He

observed

no

decrease

in

spark

length

when

he

substituted

quartz

for

glass,

as

quartz

does

not

absorb

UV

.

Through

experimentation,

he

proved

that

transverse

free

space

electromagnetic

waves

can

travel

over

some

distance
.

This

been

predicted

by

Maxwell

and

.

With

his

apparatus

configuration,

the

electric

and

magnetic

fields

would

away

from

the

wires

as

transverse

waves
.

Hertz

positioned

the

oscillator

12

meters

from

a

zinc

reflecting

plate

to

produce

standing

waves
.

Each

wave

was

4

meters
.

Using

the

ring

detector,

he

recorded

how

the

magnitude

and

wave's

component

direction

vary
.

Hertz

measured

Maxwell's

waves

and

demonstrated

that

the

velocity

of

waves

was

equal

to

the

velocity

of

light
.

The

electric

field

intensity

and

polarity

was

also

measured

by

Hertz
.

His discoveries would later be more fully understood by others and
be part of the new
"wireless age"
. In bulk, Hertz' experiments
explain
reflection
,
refraction
,
polarization
,
interference
, and
velocity

of electric waves.

Sources

http://en.wikipedia.org/wiki/Waveparticle_duality#Huygens_and_Newton

http://www.nightlase.com.au/education/optics/light.htm

http://www.juliantrubin.com/bigten/youngdoubleslit.html

http://science.hq.nasa.gov/kids/images/ems/consider.html

http://physics.tamuk.edu/~suson/html/4323/emtheory.html

http://www.juliantrubin.com/bigten/hertzexperiment.html

http://en.wikipedia.org/wiki/Heinrich_Hertz#Electromagnetic_research

http://en.wikipedia.org/wiki/Heinrich_Hertz

http://people.seas.harvard.edu/~jones/cscie129/nu_lectures/lecture6/hertz/Hertz
_exp.html