svjetlost, svuda, svjetlost oko nas -...
TRANSCRIPT
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