svjetlost, svjetlost, svjetlostsvuda okonas -...
TRANSCRIPT
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)