Transcript chap 32 - AJRomanello

Chapter 32
The Atom and the Quantum
Herriman High Physics
The Atom
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Protons – Found in the Nucleus
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Neutrons – Found in the Nucleus
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Carry a Positive Charge
Have a Mass of 1 x 10-27 kg
Carry no charge
Have a mass that is approximately the same as a
Proton
Electrons – travel around the nucleus in
specific orbits related to their energy
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Carry a negative charge
Have a mass of 9 x 10-31 kg
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Light Quanta
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Light has a dual nature – it is made up of
packets of energy called quanta or photons
which are carried on a wave.
When an atom absorbs energy electrons
move from their normal or ground state to
a higher energy or excited state. To go
back to their ground state atoms give off this
excess energy as light.
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The Energy of a Photon
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The energy of any photon of light given
off in this way is determined by the
equation:
E = hf
Where E = energy in joules
h = 6.626 x 10-34 J•s (Planck’s Constant)
f = frequency of the light
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The Photoelectric Effect
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The photoelectric effect is the
ejection of electrons from a material
when light falls upon it.
The material is sensitive to the
frequency of the light not its
intensity.
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Light as a Particle
Light as a Wave
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Light has a dual nature, it acts like a particle
and as a wave.
The fact that light can be bent by gravity
shows that light acts like a particle.
The fact that light undergoes reflection,
refraction, and diffraction shows that it
behaves like a wave.
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Reflection – turning back at a boundary
Refraction –the bending of light as it moves from
one substance to another.
Diffraction – the bending of light around an object
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Chapter 33
The Atomic Nucleus and
Radioactivity
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Nuclear Energy
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The Nucleus of an atom contains
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Protons – Positively Charged
Neutrons – no charge
Atomic Mass Number – denoted by the letter
A, this number represents the total number of
protons + neutrons in the nucleus, telling you
what isotope of the element you have.
Atomic Number – denoted by the letter Z, this
number represents the number of protons in
the nucleus, telling you what element you
have.
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Nuclear Energy
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Atomic Symbol for a
given isotope of an
element is generally
given as noted to
the right.
A prime example is
an alpha particle or
helium nucleus
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A
Z
4
2
X
He
Nuclear Reactions
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Two Types of Nuclear reactions produce
vast amounts of energy according to
Einstein’s famous equation
E = mc2
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Fission – the splitting of an atom into
smaller parts
Fusion- the joining of two small nuclei to
produce one larger nucleus
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Nuclear Reactions
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Mass defect – is the amount of mass
that is converted to energy during
fission or fusion.
Calculation of Mass defect is the
difference between the actual mass of
the atom and the known mass of each
of its parts
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Radioactivity
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Three types of Radioactivity
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Alpha – α – is the nucleus of a helium atom
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Beta – β – emission of an electron or positron
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Can be stopped by a sheet of paper, is harmful only if
ingested
Can be stopped by a sheet of lead, is harmful to all living
tissue
Gamma – γ – emission of a high energy photon
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Cannot be completely stopped. Very harmful to all living
tissue.
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Nuclear Reactions
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Alpha Decay
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Beta Decay
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Gamma Emission
226
88
Ra 
222
86
Rn  He
4
2
C  N  e 
14
6
A
Z
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14
7
N*  N  
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A
Z
Radioactive Half Life
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By definition, the amount of radioactive material
that decays to another material is determined by its
half life.
A half life is the amount of time required for ½ of
the sample to decay.
The equation for a half life is:
x
0
1
aa ( )
2
Where a0 is the amount you start with and a is the
amount you have left after x half lives.
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Sample Problem
238
92
U with a half live
If a 20 gram sample of
of 10 hours is allowed to decay for 3 days,
how much will remain at the end of that
time?
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Solution
1 x
a  a0 ( )
2
1
 20 grams( )
2
72
10
 0.136 grams
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Transmutation of Elements
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When a nucleus emits an alpha or a
beta particle it becomes a new element
– this process is called transmutation.
This can occur naturally or artifically.
This process can be useful for dating
objects, or a a tracer in medical
procedures.
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Chapter 34
Nuclear Fission and Fusion
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Applications of Nuclear Processes
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Energy can be released in a nuclear
reaction by one of two processes:
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Fission – the splitting of a nucleus into
smaller nuclei
Fusion – the joining of two smaller nucleui
into a larger nuclei
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Fission
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Fission is the breaking of a large nucleus into
smaller nuclei.
Usually caused by neutron bombardment of
the nucleus, causing the nucleus to split
Mass is converted into energy
All current nuclear reactor technology uses
fission
Fission is controlled by using a moderator, a
material which absorbs neutrons to keep the
chain reaction under control
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Fusion
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Fusion reactions take lighter nuclei, often an
isotope of hydrogen called deuterium and
fuse them together to make a heavier nuclei,
often helium
This must occur at high energy and is very
difficult to produce under laboratory
conditions
Currently no workable fusion reactor has
been produced on earth
The sun and stars all produce energy due to
nuclear fusion
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