Waves, Light, Quantum
Figure 4.1: Molar Volume
(elements known in 1869)
(a few more recently discovered elements added)
Other Periodic Trends
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View of White Light Through Spectroscope
(Investigate This 4.5)
white light viewed through slit
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light separated into different wavelengths
by diffraction grating
View of White Light Source Through
KMnO4 Solution (Investigate This 4.5)
white light source
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white light source
covered with permanganate solution
KMnO4
Color of Wavelengths Absorbed is
Complementary To Color Observed
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Purple Appearing Light
Emission vs. Absorption
(Consider This 4.7)
prism (wavelength separator)
light source
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some matter
(light absorber)
white light source
Light = Electromagnetic Waves
Electromagnetic
radiation
the emission and
transmission of energy
in the form of
electromagnetic waves
Properties of Waves
one cycle
wavelength
amplitude
= wavelength = length of one cycle
n = frequency = number of cycles/time
Properties of Waves
xn=c
c = velocity of light
wave in vacuum
= 3.00 x 108 m/s
Problem 4: A laser used to weld detached retinas
produces light with frequency of 4.69 x 1014 Hz. What
is this wavelength in nm? To what part of the electromagnetic
spectrum does this light belong? (1Hertz = 1 s-1.)
 = c/n
 = (3.00 x 108 m/s) / 4.69 x 1014 Hz
 = 6.40 x 10-7 m
 = 640 nm (red region of visible spectrum)
Waves In a Ripple Tank
(Investigate This 4.12, 4.16)


Click on ripple tank wave simulation
For 4.12


Set to Setup: Single Source; 1 Src, 1 Freq;
Color Scheme 3
For 4.16

Change Setup to Double Slit (source
automatically switches to 1 Plane Src, 1 Freq)
Planck’s Quantum Theory
Planck’s Basic Ideas

E states of a system (e.g., atom) are
quantized, not continuous
state 3
state 2
E
state 1
Classical Physics View
continuous E states
Planck’s Quantum View
quantized E states
Planck’s Basic Ideas

Only certain E increments may be
absorbed or emitted by system
state 3
state 2
E
emissions
state 1
Classical Physics View
continuous E states
infinite #of DE possible
Planck’s Quantum View
only transitions allowed are between
quantized E states
Planck’s Basic Ideas

Energy is emitted or absorbed in discrete units
(quanta)
state 3
DE = hn (Planck’s Law)
h = 6.63 x 10-34 J•s
state 2
E
state 1
DE31 = hn
The Photoelectric Effect

Light strikes metal surface and ejects an
electron
hn
e-


Classical physics predicts light intensity determines if
e- is ejected.
But e- is ejected only if light of minimum n (no) is
used; intensity does not matter.
The Photoelectric Effect
Einstein: Quantum Theory
Explains the PE Effect

Light is a stream of photons
Ephoton = hn
e-
oo e-removed
oo
oo
1
1
1
Eee- in metal
Ephoton = DEee- ejected
Ephoton > DEe-
Ephoton < DEe-
e- ejected with
kinetic energy
e- not ejected
What is no?
(What is n needed to eject e-?)

How much E must the e- absorb if it
moves from n=1 to n= ?
oo
oo


DEe- = Ee-,n=oo - Ee-,n=1
Ee-
This increase in Ee- is supplied by the
photon

DEe- = Ephoton = hno
or
no = DEe- /h
1
DE1oo = hno