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• The shorter the wavelength (), the higher the frequency ().
• Energy of the wave increases as frequency increases.
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Electromagnetic spectrum
Converting from wavelength ( to frequency ( Converting from wavelength ( to frequency (
Ex: What is the frequency of a 400 nm EM wave?
= c/ = (3.00 x 108 m/s) / (4.00 x 10-7 m) = 7.50 x 1014 Hz
c =
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Ground state: electron is at its lowest possible energy level
++
n = 1
n = 2
n = 3n = 4n = 5
Excited state: electron is above the lowest possible energy level
H1
1Photon absorbed
Photon emitted
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HydrogenHydrogen
Atomic emission spectrum of hydrogen
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Bohr atomic orbit
Quantum number
Orbit radius (nm)
Atomic energy level
Relative Energy
First n = 1 0.0529 1 E1
Second n = 2 0.212 2 E2 = 4E1
Third n = 3 0.476 3 E3 = 9E1
Fourth n = 4 0.846 4 E4 = 16E1
Fifth n = 5 1.32 5 E5 = 25E1
Sixth n = 6 1.90 6 E6 = 36E1
Seventh n = 7 2.59 7 E7 = 49E1
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For emission: E = Ehigher – Elower = Ephoton = h = hc/
= frequency (Hz) h = Planck’s constant (6.63 x 10-34 J·s)
= wavelength (m) c = speed of light (3.00 x 108 m/s)
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Examples
1. What is the energy of a green photon having a wavelength of 514 nm?
E = hc/ = (6.626 x 10-34 J·s)(3.00 x 108 m/s)
5.14 x 10-7 m
= 3.87 x 10-19 J
2. What is the frequency of the photon in #1?
= c/ = (3.00 x 108 m/s) / (5.14 x 10-7 m) = 5.84 x 1014 Hz
3. What is the frequency of a photon that has an energy of 3.31 x 10-27 J?
= E/h = (3.31 x 10-27 J) / (6.626 x 10-34 J·s) = 5.00 x 106 Hz
(use c = )
(use E = h)
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Some people say I have a dual personality!
Hi, I’m a photon!
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Wave nature of light
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Diffraction: the bending of waves around an object
Diffraction around an obstacle
Diffraction through an opening
Diffraction around a corner
The amount of diffraction that occurs depends upon the size of the obstacle or opening and the wavelength of the incident wave
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Electromagnetic waves
Both electrical charges and magnets have fields around them.
An electromagnetic wave is a double transverse wave that consists of both an electric and a magnetic field wave
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Electromagnetic waves are transverse waves because the electric and magnetic fields vibrate in a direction perpendicular to the direction of travel.
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http://lectureonline.cl.msu.edu/~mmp/kap28/PhotoEffect/photo.htm
Photoelectric Effect
e
e e
e
Na metal
V
‘Particles’ of light are called photons
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If light can have characteristics of BOTH particles and waves…
…can particles of matter also behave like waves?
mvh
De Broglie’s equation
h = 6.63 x 10-34 J·s
m = mass in kg
v = velocity in m/s
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6.0 x 1024 kg2.8 x 104 m/s
e
9.1 x 10-31 kg3.0 x 108 m/s
5.7 x 10-2 kg53 m/s
(Venus Williams, 1998)
h = 6.63 x 10-34 J·s
m = mass in kg
v = velocity in m/smvh
What is the wavelength of these three ‘particles’?