atom and light astr 14: exploring the universe. 2 outline nature of light basic properties of light...
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Atom and Light
ASTR 14: Exploring the Universe
2
Outline
• Nature of Light
• Basic Properties of Light
• Atomic Structure
• Periodic Table of the Elements
• Three Types of Spectra
• Interaction of Light and Matter
• Useful Application – Doppler Effect
3
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
4
Wave Properties of Light
• Wave Properties– diffraction– Interference
• Young’s Double-Slit Experiment (1801)
5
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)
6
Electromagnetic Spectrum
• Speed of Light = wavelength x frequency
• C = x
7
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.
8
Blackbody Radiation
9
Blackbody Radiation
• Wien’s Law– The wavelength of
maximum emission of a blackbody is inversely proportional to its temperature.
• Stefan-Boltzmann Law (Box 5-2)– The energy flux (power
per unit area) of a blackbody is proportional to the 4th power of its temperature.
)(
0029.0)(max KTm
42842 1067.5;)( KWmxTWmFlux
10
Atomic Structure
• Rutherford’s Experiment (1910)
• Rutherford’s Model of the Atom
• Atomic Structure– cloud of electrons– nucleus
• protons• neutrons
11
Atomic Structure
12
13
Three Types of Spectra
14
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.
15
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.
16
Interaction of Light and Matter
Electron Transitions in Hydrogen
17
Interaction of Light and Matter
18
Interaction of Light and Matter
States of Matter
19
An Example
20
Doppler Effect
• 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.
c
v
o
= wavelength shift
o = lab wavelength
V = radial velocity
c = speed of light
+ = redshift
- = blueshift
21
Doppler Effect
Stationary Source Moving Source
22
An Example
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