Svjetlost, svuda, svjetlost oko nas

(pardon, elektromagnetsko zračenje)

Uvod u spektroskopiju Predavanje 2

Osnove optike

Što je to svjetost?

I. I. Newton (1704 g.) "Opticks”

Čestice (korpuskule)

Svjetlost se sastoji od “čestica”.

Prizma (1666 g.)

Reflektirajuci teleskop (1668 g.)

Teorija boje

Duga

Newtonov genije;

objašnjenje niza fenomena

II. Christian Huygens “Traité de la Lumière”

→ valna (undularna) teorija svjetlosti,

no bez exp.

Svjetlost Kraj XVIII. stoljeća i početak XIX. stoljeća

Novi eksperimenti (Young, Fresnel, Arago, Helmholtz,

Fraunhofer,...)

difrakcija (ogib) Y

interferencija Y

polarizacija F

svjetlost je VAL

transverzalni! F

(Y – mala t komp, velika

l komp; F – samo t komp)

Svjetlost Kraj XVIII. stoljeća i početak XIX. stoljeća

Novi eksperimenti (Young, Fresnel, Arago, Helmholtz,

Fraunhofer,...)

difrakcija (ogib) Y

interferencija Y

polarizacija F

svjetlost je VAL

transverzalni! F

(Y – mala t komp, velika

l komp; F – samo t komp)

isti Young: - Youngov modul elasticnosti - Young + Champollion = prijevod kamena iz Rosete - osnivac fizioloske optike: prilagodba oka na udaljenost objekta, asti- gmatizam - teorija kapilarnosti - hemodinamika; “rule of thumb” za doziranje lije- kova kod djece - “Languages”: uspored- ba 400 jezika; pojam Indo-europski jezici - “Young temperament”: metoda za “tuniranje” instr.

Robinson, Andrew (2007). The Last Man Who Knew Everything:

Thomas Young, the Anonymous Genius who Proved Newton

Wrong and Deciphered the Rosetta Stone, among Other

Surprising Feats. Penguin.

Thomas Young (E) (13 June 1773 – 10 May 1829)

Augustin-Jean Fresnel (F) (10 May 1788 – 14 July 1827)

François Arago (F) (26 Feb. 1786 – 2 Oct. 1853)

Hermann von Helmholtz (G) (31 August 1821 – 8 Sept. 1894)

Joseph von Fraunhofer (G) (6 March 1787 – 7 June 1826)

Sir Isaac Newton (E) (4 January 1643 – 31 March 1727)

Longitudinalni valovi

Gibanje čestica U SMJERU

širenja vala (zvuk, kuglice na

koncu, valovi u cvrstom tijelu)

Transverzalni valovi

Gibanje čestica OKOMITO na smjer širenja vala

(valovi na vodi, valovi u cvrstom tijelu, ”spaga”)

Elektromagnetski valovi???

Table 1: Seismic Waves

Wave Type

(and names)

Particle Motion Typical Velocity Other Characteristics

P, Compressional

, Primary,

Longitudinal

Alternating compressions

(“pushes”) and dilations (“pulls”)

which are directed in the same

direction as the wave is

propagating (along the ray

path); and therefore,

perpendicular to the wavefront.

VP ~ 5 – 7 km/s in typical

Earth’s crust; >~ 8 km/s in

Earth’s mantle and core;

~1.5 km/s in water; ~0.3

km/s in air.

P motion travels fastest in materials, so the P-

wave is the first-arriving energy on a

seismogram. Generally smaller and higher

frequency than the S and Surface-waves. P

waves in a liquid or gas are pressure waves,

including sound waves.

S, Shear,

Secondary,

Transverse

Alternating transverse motions

(perpendicular to the direction

of propagation, and the ray

path); commonly approximately

polarized such that particle

motion is in vertical or horizontal

planes.

VS ~ 3 – 4 km/s in typical

Earth’s crust;

>~ 4.5 km/s in Earth’s

mantle;

~ 2.5-3.0 km/s in (solid)

inner core.

S-waves do not travel through fluids, so do not

exist in Earth’s outer core (inferred to be

primarily liquid iron) or in air or water or molten

rock (magma). S waves travel slower than P

waves in a solid and, therefore, arrive after the

P wave.

L, Love,

Surface waves, Long

waves

Transverse horizontal motion,

perpendicular to the direction of

propagation and generally

parallel to the Earth’s surface.

VL ~ 2.0 - 4.4 km/s in the

Earth depending on

frequency of the

propagating wave, and

therefore the depth of

penetration of the

waves. In general, the

Love waves travel slightly

faster than the Rayleigh

waves.

Love waves exist because of the Earth’s

surface. They are largest at the surface and

decrease in amplitude with depth. Love waves

are dispersive, that is, the wave velocity is

dependent on frequency, generally with low

frequencies propagating at higher

velocity. Depth of penetration of the Love

waves is also dependent on frequency, with

lower frequencies penetrating to greater depth.

R, Rayleigh,

Surface waves, Long

waves, Ground roll

Motion is both in the direction of

propagation and perpendicular

(in a vertical plane),

and “phased” so that the

motion is generally elliptical –

either prograde or retrograde.

VR ~ 2.0 - 4.2 km/s in the

Earth depending on

frequency of the

propagating wave, and

therefore the depth of

penetration of the waves.

Rayleigh waves are also dispersive and the

amplitudes generally decrease with depth in the

Earth. Appearance and particle motion are

similar to water waves. Depth of penetration of

the Rayleigh waves is also dependent on

frequency, with lower frequencies penetrating to

greater depth.

Partial cross section of the Earth showing major layer boundaries, approximate P-wave seismic velocities (Vp), and approximate ray path for P- and S-waves from a shallow earthquake to a seismograph at about 18 degrees (~2000 km) distance. (http://web.ics.purdue.edu/~braile/edumod/waves/WaveDemo.htm)

Elektromagnetski valovi

Transverzalni valovi – gibanje čestica (medija)

OKOMITO na smjer širenja vala

Čestice, medij??? (kraj XIX. stoljeća)

“Eter” medij u kojem se sire el. mag. valovi

Niz eksperimenata (M&M – 1887.) & Einstein:

nema etera

Maxwellove jednadžbe – teorijska

pretpostavka (1864.)

Herzov (umro s 36 g.) eksperiment –

eksperimentalna potvrda (1887.)

“It's of no use whatsoever[...] this is just an experiment that proves Maestro

Maxwell was right - we just have these mysterious electromagnetic waves that we

cannot see with the naked eye. But they are there.”

ELEKTROMAGNETSKI valovi

imaju valna svojstva

(ogib, interferencija)

Cesticna svojstva, „komad” energije

foton

Dualna priroda svjetlosti

(I. Supek, M. Furic, “Pocela fizike”,

Skolska knjiga, Zagreb (1994))

Pitanje: Koja dva eksperimenta pokazuju valno-cesticnu

prirodu svjetlosti?

c

h

Dualna priroda svjetlosti

http://dev.physicslab.org/Document.aspx?doctype=3&filename=AtomicNuclear_DualNature.xml

http://phet.colorado.edu/simulations/sims.php?sim=Photoelectric_Effect

Moze li se fotoelektricni efekt objasniti

valnom prirodom svjetlosti?

Zasto?

Spektroskopija (Fraunhofer)

Bavi se elektromagnetskim zračenjem.

Što je spektar?

Ovisnost intenziteta svjetlosti iz nekog izvora o valnoj duljini.

Spektar Sunca

Zasto se onda Sunce cini zutim?

Što je spektar?

Ovisnost intenziteta svjetlosti iz nekog izvora o valnoj duljini.

Spektar Sunca

• Spektroskopija: atomska i molekularna

Vrste spektara:

kontinuirani – nema spektralnih linija

apsorpcijski – tamne linije na kontinuiranom spektru

emisijski – izolirane linije

• Spektroskopija: atomska i molekularna

Vrste spektara:

kontinuirani – nema spektralnih linija

apsorpcijski – tamne linije na kontinuiranom spektru

emisijski – izolirane linije

Izvori svjetlosti

Diskretni prijelazi → Linijski spektri atoma

Fraunhofer, (L. Ponomarev “Kvantna kocka”, Moderna fizika, Zagreb)

Izvori svjetla

Zračenje crnog tijela

Emitirano zračenje kao

funkcija valne duljine

Emitirano zračenje ovisi o

TEMPERATURI.

Mi bi “željeli” Sunce; 6000 K

Izvori svjetla

Zračenje crnog tijela

Gorenje (temperatura)

Lime light (zagrijani vapnenac)

Žarulja (žari) ovisno temperaturi

dobivamo zračenje (1802.)

ako radi na višoj temperaturi imamo

“bijelo” svjetlo

Halogene žarulje (inertni plin + I ili Br)

→ pomak prema plavom (1882.)

http://www.handprint.com/HP/WCL/color12.html

Izvori svjetla

Zračenje crnog tijela

Gorenje (temperatura)

Lime light (zagrijani vapnenac)

Žarulja (žari) ovisno temperaturi

dobivamo zračenje (1802.)

ako radi na višoj temperaturi imamo

“bijelo” svjetlo

Halogene žarulje (inertni plin + I ili Br)

→ pomak prema plavom (1882.)

http://www.handprint.com/HP/WCL/color12.html

Emitirano zračenje ovisi o

TEMPERATURI.

Mi bi “željeli” Sunce; 6000 K

I mi zračimo!!!!

Spektar Sunca ↔ spektar crnog tijela

Ima li bolje crno tijelo od Sunca?

“Planckian locus”

Ima li bolje crno tijelo od Sunca?

grafit

Ni-P slitine (e = 0.97)

zid karbonskih nanocjevcica (e = 0.99)

Spektar Sunca ↔ spektar crnog tijela

http://www.nanoscience.gatech.edu/pape

r/1999/99_PMB_2.pdf

Zakoni zracenja crnog tijela

"On the Law of Distribution of Energy in the Normal Spectrum". Annalen der Physik 4 (1901)

Rayleigh-Jeansov zakon

4

2)(

ckTTB

Planckov zakon

1

2)(

5

2

kT

hc

e

hcTB

Wienov zakon (pomaka)

bTm

Stefan-Boltzmannov zakon

32

45

4*

15

2

hc

k

Tj

Spektar i boja

nejednoznačnost

istu boju možemo dobiti

raznim spektralnim

raspodjelama!

metamerizam

(spektrofotometar rjesava

stvar)

http://graphics.cs.brown.ed

u/research/exploratory/free

Software/repository/edu/br

own/cs/exploratories/apple

ts/spectrum/metamers_gui

de.html

http://graphics.stanford.ed

u/courses/cs178/applets/c

olormatching.html