Download Modern Physics - Northwest ISD Moodle

Modern Physics
Wave-Particle Duality
Model of the atom
Radioactivity / Four Forces of nature
Wave-Particle Duality
• When tested as if it were a wave, light behaves like a wave.
Light will:
– Diffract
– Refract
– Exhibit interference
– Polarize
– exhibit the Doppler effect (ex. Red shift)
• When tested as a particle, light behaves like a particle (ex. the
photoelectric effect).
The nucleus of the atom
• The neutrons and protons are
grouped together in the nucleus,
which is at the center of the atom.
• If the atom were the size of your
classroom, the nucleus would be
the size of a single grain of sand in
the center of the room.
• Most of an atom’s mass is
concentrated in the nucleus.
Scientists describe all of nature with
only four forces.
• Gravitational force
• Weak Nuclear force
• Electromagnetic force
• Strong nuclear force
• It is important to note that scientists do no know why these forces
exist or what causes them. We only observe their effects and
propose they are there.
Electromagnetic Force
• The force is the attraction
between protons (positive)
and electrons (negative).
• Electrons are bound to the
nucleus by electromagnetic
forces.
 The momentum of the electron causes it to move
around the nucleus rather than falling straight in.
Strong Nuclear Force
• Holds the nucleus of an atom together
• Attracts neutrons and protons to each
other, otherwise the positively charged
protons would repel each other.
Weak Nuclear Force
• Causes a neutron to break into a proton and an
electron producing a new element
• Weaker than both the electric force and the strong
nuclear force.
• Causes radioactive decay
• Only occurs at the subatomic level
• The force of gravity causes objects to be attracted to
each other
 Every process we
know in the universe
can be explained in
terms of these
fundamental forces.
Marie Curie – Nobel prize winner
• The word radioactivity was
first used by Marie Curie in
1898.
• She used the word
radioactivity to describe the
property of certain
substances to give off
invisible “radiations” that
could be detected by films.
Radioactive Decay
• Three different kinds of
radiation given off by
radioactive materials:
– Alpha rays
– Beta rays
– Gamma rays
• called “rays” because the
radiation carried energy and
moved in straight lines, like
light rays.
• Radioactivity comes
from the nucleus of the
atom.
• If the nucleus has too
many neutrons, or is
unstable the atom
undergoes radioactive
decay.
• decay - to "break
down."
Atomic Decay
• Alpha decay: the nucleus ejects two protons and two
neutrons.
• Beta decay: a neutron in the nucleus splits into a proton
and an electron.
• Gamma decay occurs because the nucleus is at too high
an energy. The nucleus falls down to a lower energy state
and, in the process, emits a high energy photon.
• Radioactive decay gives off energy.
• The energy comes from the conversion of
mass into energy.
• Because the speed of light (c) is such a
large number, a tiny bit of mass generates
a huge amount of energy.
• Radioactivity occurs because everything
in nature tends to move toward lower
energy.
Radiation
• The flow of energy through space.
• Forms of radiation:
– Light
– Radio
– Microwaves
– X-rays
• Many people mistakenly think of radiation as
only associated with nuclear reactions.
X-ray machines
• X-rays are photons
• Used to produce
images of bones and
teeth on x-ray film.
• X-ray film turns black
when exposed to xrays.
X-Rays Uses
• High level therapeutic
x-rays are used to
destroy diseased tissue,
such as cancer cells.
• The beams are made to
overlap at the place
where the doctor wants
to destroy diseased
cells.
CAT scan
• Computerized Axial
Tomography
• Produced by a computer that
controls an x-ray machine as it
takes pictures of the body from
different angles.
• Produces three-dimensional
images of bones and other
structures within the body.
Radiation Detection
The Geiger counter is
a type of radiation
detector invented to
tell when radiation is
present and to
measure its
intensity.
Fusion reactions
• Nuclear reaction that
combines, or fuses, two
smaller nuclei into a
larger nucleus.
• It is difficult to make
fusion reactions occur
because positively
charged nuclei repel each
other.
Fission reactions
• A fission reaction splits
up a large nucleus into
smaller pieces.
• A fission reaction
typically happens
when a neutron hits a
nucleus with enough
energy to make the
nucleus unstable.
Nuclear Reactions and Energy
• A nuclear reaction is any process that
changes the nucleus of an atom.
• Radioactive decay is one form of
nuclear reaction.
Nuclear Reactions and Energy
• If you could take apart a nucleus and separate
all of its protons and neutrons, the separated
protons and neutrons would have more mass
than the nucleus did.
• The mass of a nucleus is reduced by the energy
that is released when the nucleus comes
together.
• Nuclear reactions can convert mass into energy.
Nuclear Reactions and Energy
• Both these nuclear reactions release a small
portion of the mass as large amounts of
energy.
• Nuclear fusion is what powers a modern
nuclear warhead.
• Nuclear fission (less powerful) occurs in an
atomic bomb (like the ones used against Japan
in WWII), or in a nuclear power plant.
Mass Energy Equivalence
The energy released can be calculated using the equation:
E = mc2
Where:
E
m c2
E = energy released (J)
m = mass difference (kg)
c = speed of light in a vacuum (3 x 108 m/s)