It’s a wave, It’s a particle, Its Electron Boy!!!!!
Light emission is understood with
the familiar planetary model of the
atom. (Bohr’s Model)
 Each element has a number of
electrons that occupy the shells
surrounding its nucleus, each
element also has its own pattern of
electron shells, or energy states.
 These states are found only at
certain energies; we say they are
exact, whole. We call these steady
states quantum states.


When energy is absorbed by an element, an
electron may be boosted to a higher energy
level. The atom is said to be excited. Later, it
returns to its original level.
Fluorescence

Many materials excited by ultraviolet light emit
visible light upon de-excitation.

Many substances undergo excitation when
illuminated with ultraviolet light.
Incandescent lamp
A glass enclosure with a filament of tungsten,
through which an electric current is passed.
 The hot filament emits a continuous spectrum,
mostly in the infrared, with smaller visible part.
 The glass enclosure prevents oxygen in air from
reaching the filament, to prevent burning up by
oxidation.
 Argon gas with a small amount of a halogen is
added to slow the evaporation of tungsten.
 The efficiency of an incandescent bulb is 10%

Fluorescent lamps

UV emitted by excited gas strikes phosphor material
that emits white light.
Compact fluorescent lamps (CFL)
 Miniaturize a fluorescent tube,
wrap it into a coil, and outfit it
with the same kind of plug a
common incandescent lamp has,
and you have a compact
fluorescent lamp (CFL).
 CFLs are more efficient than
incandescent lamps, putting out
about 10 times more light for the
same power input.
 A downside to the CFL is its
mercury content, which poses
environmental disposal
problems.
A photoelectric effect is
any effect in which light
energy is converted to
electricity.
Light shining on the negatively charged, photosensitive
metal surface liberates electrons.
 The liberated electrons are attracted to the positive
plate and produce a measurable current.
 Current can be sent out as electrical power or used to
run other motors and machines as needed.

The photoelectric effect (continued)
The photoelectric effect (continued)



Light behaves like a wave when it diffracts
and refracts.
Light behaves like a particle when it knocks
other electrons away from certain metals.
This is called the Wave - Particle Duality of
Light.
Scanning Electron Microscope uses the wave nature of electrons
to create images similar to the image of the mosquito shown
here.
A streetlight is a good example of an application of
photoconductivity.
As daylight
fades, the
electrical current
in the
streetlight’s
semiconductor
stops. This
activates a
switch that turns
the streetlight
on.
Solar panels are nothing
more than a series of
metallic plates that face
the Sun and exploit the
photoelectric effect. The
light from the Sun will
liberate electrons, which
can be used to heat your
home, run your lights, or,
in sufficient enough
quantities, power
everything in your home.
Source: www.futureenergy.org/ picsolarpannelsmatt.jpg
Radioactivity
 Radioactivity is the process of nuclear decay
(radioactive decay).
 Nothing new in the environment; it’s been going on
since time zero.
 It warms Earth’s interior, is in the air we breathe,
and is present in all rocks (some in trace amounts).
 It is natural.
Radioactive elements
emit three distinct types
of radiation:
•  —alpha: positively
charged (helium
nuclei)
•  — beta: negatively
charged (electrons)
•  —gamma
(electromagnetic
radiation)
• n - neutron
Relative penetrations
A typical uranium fission reaction:
Note the mass number as well as atomic
numbers balance.
Chain reaction—a self-sustaining
reaction in which the products of one
reaction event stimulate further
reaction events
Chain reaction in
uranium
Small amount,
chain reaction
fizzles.
 Critical amount,
chain reaction
produces an
explosion.

Nuclear fission reactors



About 20% of electric energy in
the United States is generated
by nuclear
fission reactors.
More in some other countries—
about
75% in France.
Reactors are simply nuclear
furnaces that boil water to
operate steam-driven
generators.
 Nuclear fusion is the opposite of
nuclear fission.
 Fission: nuclei “fizz” apart.
 Fusion: nuclei fuse together.
Typical fusion reactions: