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Transcript
Atom and Light
Lancelot L. Kao
Updated: Jan 24, 2010
Outline
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Nature of Light
Basic Properties of Light
Three Types of Spectra
Useful Application – Doppler Effect
Atomic Structure
Periodic Table of the Elements
Interaction of Light and Matter
Blackbody Radiation
States/Phases of Matter
2
Nature of Light
• What is the “Nature” of Light?
• Observed Properties of Light
– reflection, refraction, diffraction, & interference
• Wave Properties
– reflection, refraction, diffraction, & interference
• Particle Properties
– reflection, refraction
• Particle-Wave Duality
3
Wave Properties of Light
• Wave Properties
– diffraction
– Interference
• Young’s Double-Slit
Experiment (1801)
4
Wave Properties of Light
• Electromagnetic
Waves
– wavelength (meter)
– frequency (cycles per
second = Hertz = Hz)
• Speed of Light
– constant within a
medium
– absolute speed
– 3.0 x 108 m/s in
vacuum
Fizeau-Foucault Method (1850)
5
Electromagnetic Spectrum
• Speed of Light =
wavelength x
frequency
• C=lxn
6
Particle Properties of Light
• Max Planck (1900)
– Blackbody Radiation
– Electromagnetic energy
(radiation) is emitted in
discrete, particlelike
packet.
• Albert Einstein (1905)
– Re-interpret Planck’s result
– Photoelectric Effect
– Light as particles -photons
• Energy of a Photon
– The energy of a photon is
proportional to its
frequency.
7
Three Types of Spectra
8
Interaction of Light and Matter
• Kirchoff’s 1st Law
– A hot opaque body, such as a perfect blackbody, or a hot, dense
gas produces a continuous spectrum.
• Kirchoff’s 2nd Law
– A hot, transparent gas produces an emission line spectrum.
• Kirchoff’s 3rd Law
– A cool, transparent gas in front of a source of a continuous
spectrum produces an absorption line spectrum. The
absorption lines in the absorption line spectrum of a particular
gas occur at exactly the same wavelengths as the emission lines
in the emission line spectrum of the same gas.
• Types of spectra of matter can produce is dictated by the
physical condition/state of the matter.
9
Doppler Effect
l = wavelength shift
l
v

lo c
lo = lab wavelength
V = radial velocity
c = speed of light
+ = redshift
- = blueshift
•
•
•
Christian Doppler (1842)
The apparent change in wavelength or frequency of radiation due to relative
motion between the source and the observer along the line-of-sight.
If the relative motion between the source and the observer is moving away
from each other, the observed spectral line is longer than the lab
wavelength, it is called a redshift. If the relative motion between the source
and the observer is moving towards each other, the observed wavelength is
shorter than the lab wavelength, it is called a blueshift.
10
Doppler Effect
Stationary Source
Moving Source
11
An Example
12
Relativistic Doppler Effect
lobserved
lo
v
1
c

v
1
c
lobserved = observed
wavelenght
lo = lab wavelength
v = radial velocity
c = speed of light
+ = redshift
- = blueshift
13
Atomic Structure
• Rutherford’s
Experiment (1910)
• Rutherford’s Model of
the Atom
• Atomic Structure
– cloud of electrons
– nucleus
• protons
• neutrons
14
Atomic Structure
15
16
Interaction of Light and Matter
• Bohr Model of Hydrogen Atom
– energy levels or states
• Quantum Rules
– Electron can only occupy at discrete energy level.
– Electron can jump from one energy level to another only if it
gains or loses a specific amount of energy equal to the
differences of the levels.
17
Interaction of Light and Matter
Electron Transitions in Hydrogen
18
Interaction of Light and Matter
19
Blackbody Radiation
20
Blackbody Radiation
• Wien’s Law
– The wavelength of
maximum emission of a
blackbody is inversely
proportional to its
temperature.
0.0029
lmax (m) 
T (K )
• Stefan-Boltzmann Law
– The energy flux (power
per unit area) of a
blackbody is proportional to
the 4th power of its
temperature.
2
Flux(Wm )  sT 4 ;s  5.67 x108Wm 2 K 4
21
An Example
22
Interaction of Light and Matter
States of Matter
23