Svjetlost, svjetlost, svjetlost svuda oko nas

(pardon, elektromagnetsko zračenje)

Atomska fizika i spektroskopija Predavanje 2

Osnove optike

Što je to svjetost?

I. Newton (167x g.) "Opticks”Čestice (korpuskule)Svjetlost se sastoji od “čestica”.

Prizma Teorija boje Duga

Newtonov genije;objašnjenje niza fenomenapoput duge

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, velikal komp; F – samo t komp)

isti Young:- Youngov modulelasticnosti- Young + Champollion= prijevod kamena iz Rosete- osnivac fizioloskeoptike: prilagodba oka naudaljenost objekta, asti-gmatizam- teorija kapilarnosti- hemodinamika; “rule ofthumb” za doziranje lije-kova kod djece- “Languages”: uspored-ba 400 jezika; pojamIndo-europski jezici- “Young temperament”:metoda za “tuniranje” instr.

Robinson, Andrew (2007). The Last Man Who Knew Everything: Thomas Young, the Anonymous Genius who Proved NewtonWrong and Deciphered the Rosetta Stone, among OtherSurprising 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???

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.

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.

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.

R, Rayleigh, Surface waves, Long waves, Ground roll

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.

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.

Transverse horizontal motion, perpendicular to the direction of propagation and generally parallel to the Earth’s surface.

L, Love, Surface waves, Long waves

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.

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.

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.

S, Shear, Secondary, Transverse

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.

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.

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.

P, Compressional, Primary, Longitudinal

Other CharacteristicsTypical VelocityParticle MotionWave Type (and names)

Table 1: Seismic Waves

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 pretpostavkaHerzov (umro s 36 g.) eksperiment – eksperimentalna potvrda

“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 theyare there.”

FizikaFizika svjetlostisvjetlosti

•• svjetlosvjetlo kaokao cesticacestica = = fotonifotoni

velikavelika λλmala mala υυmala Emala E

malimali λλvelikavelika υυvelikavelika EE

ELEKTROMAGNETSKI valoviimaju valna svojstva(ogib,interferencija)

čestična 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?

λν=λν=λν=λν=c

Ε=Ε=Ε=Ε=hνννν

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 i Spektroskopija i atomskaatomska fizikafizika

VrsteVrste spektaraspektara::

�� kontinuiranikontinuirani –– nemanema spektralnihspektralnih linijalinija

�� apsorpcijskiapsorpcijski –– tamnetamne linijelinije nana kontinuiranomkontinuiranom spektruspektru

�� emisijskiemisijski –– izoliraneizolirane linijelinije

•• Spektroskopija i Spektroskopija i atomskaatomska fizikafizika

VrsteVrste spektaraspektara::

�� kontinuiranikontinuirani –– nemanema spektralnihspektralnih linijalinija

�� apsorpcijskiapsorpcijski –– tamnetamne linijelinije nana kontinuiranomkontinuiranom spektruspektru

�� emisijskiemisijski –– izoliraneizolirane linijelinije

Izvori svjetlostiDiskretni prijelazi Linijski spektri atoma

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

Izvori svjetlaZračenje crnog tijela

Emitirano zračenje kao funkcija valne duljine

Emitirano zračenje ovisi o TEMPERATURI.Mi bi “željeli” Sunce; 6000 K

Izvori svjetlaZračenje crnog tijela

� Gorenje (temperatura)� Lime light (zagrijani vapnenac)� Žarulja (žari) ovisno temperaturidobivamo zračenje (spektar)� Ako radi na višoj temperaturi imamo “bijelo” svjetlo� Halogene žarulje (inertni plin + I ili Br)→ pomak prema plavomhttp://www.handprint.com/HP/WCL/color12.html

Izvori svjetlaZračenje crnog tijela

� Gorenje (temperatura)� Lime light (zagrijani vapnenac)� Žarulja (žari) ovisno temperaturidobivamo zračenje (spektar)� Ako radi na višoj temperaturi imamo “bijelo” svjetlo� Halogene žarulje (inertni plin + I ili Br)→ pomak prema plavomhttp://www.handprint.com/HP/WCL/color12.html

Emitirano zračenje ovisi o TEMPERATURI.Mi bi “željeli” Sunce; 6000 K

I mi zraI mi zraččimo!!!!imo!!!!

I mi zraI mi zraččimo!!!!imo!!!!

Spektar Sunca ↔ spektar crnog tijela

Ima li bolje crno tijelo od Sunca?

Spektar Sunca ↔ spektar crnog tijela

Ima li bolje crno tijelo od Sunca?

� grafit� Ni-P slitine (e = 0.97)� zid karbonskih nanocjevcica (e = 0.99)

“Planckianlocus”

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)(

λλckT

TB =

Planckov zakon

1

2)(

5

2

−=

kT

hc

e

hcTB

λλ λ

Wienov zakon (pomaka)

bTm =λ

Stefan-Boltzmannov zakon

32

45

4*

15

2

hc

k

Tj

πσ

σ

=

=

Spektar i boja

� nejednoznačnost

� Istu boju možemo dobiti raznim spektralnim raspodjelama !!!!

� metamerizam(spektrofotometar rjesavastvar)