Transcript From here things get fuzzy.

MODERN PHYSICS
By 1932, the basic building blocks of matter were known:
p+
e-
n
The Bohr model of the atom was the basis for our understanding of what the
solar system atom looked like:
e-
p+
n
p+
e-
n
This is what you learned in elementary school. This is wrong, but at least we
can understand it.
e-
p+
n
p+
e-
n
There were (are) other questions, like “What is the neutron / proton /electron
made of?
e-
p+
n
p+
e-
n
What we know:
Conservation of charge
Conservation of mass
Conservation of energy
Conservation of momentum
eThese laws are confirmed by every experiment
that has been performed.
p+
n
p+
e-
n
What we know:
From here things get fuzzy.
Conservation of charge
Conservation of mass
Conservation of energy
Conservation of momentum
e-
p+
n
p+
e-
n
What we know:
From here things get fuzzy.
Conservation of charge
me = 9.11 × 10^(–31) kg
Conservation of mass
mp = 1.6726 x 10^(-27) kg
Conservation of energy
mn = 1.6749 x 10^(-27) kg
Conservation of momentum
e-
2p = 3.3452 x 10^(-27) kg
2n = 3.3498 x 10 ^-27kg
-------------------------------6.6945 x 10^(-27)kg
p+
n
p+
mHE = 6.6447 × 10^(−27)kg
Difference (“mass defect”) =
0.0498 x 10^(-27)kg
e-
n
When He forms, 28MeV is released.
Using Einstein’s E = mc^2,
E = mc^2 = 0.0498 x E-27kg * (3E8)^2 = 4.482E-12 J = 28E6 eV = 28MeV
The difference in mass between the sum of the masses of the neutrons and protons
in a Helium-4 nucleus is 28 MeV.
Fusion!
Essentially all of the energy of the universe comes from the
fusion of hydrogen into helium and the resulting
release of energy.
e-
~28MeV per helium atom in the process.
p+
n
p+
e-
n
Light atoms tend to combine and release energy as they do so.
Heavy atoms tend to split and release energy as they do so. Uranium and Plutonium are
particularly useful in this regard, and are the basis of nuclear fission.
Heavy nuclei break into
lighter nuclei and energy is
released.
Light nuclei fuse into heavy
nuclei and energy is
released.
Light atoms tend to combine and release energy as they do so.
Heavy atoms tend to split and release energy as they do so. Uranium and Plutonium
are particularly useful in this regard, and are the basis of nuclear fission.
Note there are
three neutrons
released for every
incident neutron.
This is the basis of a
chain reaction.
http://www.youtube.com/watch?v=JxzPN-vdP_0&feature=related
Let’s look at a neutron sitting by itself in space. After ~15 minutes, the
neutron has a 50% probability of decaying to a proton plus an electron:
p+
n
Starting
position
Decay
products
e-
Note that:
1) Charge is conserved
2) Mass + energy is (almost)
conserved
3) What is wrong with this picture?
4) Momentum is NOT conserved!
Let’s look at a neutron sitting by itself in space. After ~15 minutes, the
neutron has a 50% probability of decaying to a proton plus an electron:
Neutrons look like they
have internal “stuff”
rather than just being a
simple round blob…
p+
Decay
products
Neutrino
e-
Note that:
No charge
1) Charge is conserved
Momentum
2) Mass + energy is (almost) conserved
3) What is wrong with this picture?
Very tiny
mass
v~c
4) With the addition of the neutrino,
momentum is conserved.
What is inside a Proton or a Neutron? QUARKS!
The internal structure
of the neutron gives
rise to all this stuff
when it decays.
p+
Decay
products
n
e-
Electrons don’t stay in pretty “orbits”, either. We like to think of
electrons as particles, but they also act like waves and spend part of
the time inside the nucleus!
e
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p+
n
n
p+
e
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5.3b Charge is quantized on two levels. On the atomic level, charge is restricted to
multiples of the elementary charge (charge on the electron or proton). On the
subnuclear level, charge appears as fractional values of the elementary charge
(quarks).
5.3f Among other things, mass-energy and charge are conserved at all levels (from
subnuclear to cosmic).
5.3j The fundamental source of all energy in the universe is the conversion of mass
into energy.*
5.3g The Standard Model of Particle Physics has evolved from previous attempts to
explain the nature of the atom and states that: • atomic particles are composed of
subnuclear particles • the nucleus is a comglomeration of quarks which manifest
themselves as protons and neutrons • each elementary particle has a corresponding
antiparticle
observe and explain energy conversions in real-world situations recognize and
describe conversions among different forms of energy in real or hypothetical devices
such as a motor, a generator, a photocell, a battery
4.1b Energy may be converted among mechanical, electromagnetic, nuclear, and
thermal forms.
4.3a An oscillating system produces waves. The nature of the system determines the
type of wave produced. 4.3b Waves carry energy and information without
transferring mass. This energy may be carried by pulses or periodic waves. 4.3d
Mechanical waves require a material medium through which to travel. 4.3g
Electromagnetic radiation exhibits wave characteristics. Electromagnetic waves can
propagate through a vacuum. 4.3j The absolute index of refraction is inversely
proportional to the speed of a wave.* 4.3k All frequencies of electromagnetic
radiation travel at the same speed in a vacuum.* 4.3l Diffraction occurs when waves
pass by obstacles or through openings. The wavelength of the incident wave and the
size of the obstacle or opening affect how the wave spreads out.
4.3 Explain variations in wavelength and frequency in terms of the source of the
vibrations that produce them, e.g., molecules, electrons, and nuclear particles. iv.
differentiate between transverse and longitudinal waves
5.3a States of matter and energy are restricted to discrete values (quantized). 5.3c On
the atomic level, energy is emitted or absorbed in discrete packets called photons.*
5.3 Compare energy relationships within an atom’s nucleus to those outside the
nucleus. i. interpret energy-level diagrams ii. correlate spectral lines with an energylevel diagram
5.3h Behaviors and characteristics of matter, from the microscopic to the cosmic
levels, are manifestations of its atomic structure. The macroscopic characteristics of
matter, such as electrical and optical properties, are the result of microscopic
interactions. 5.3i The total of the fundamental interactions is responsible for the
appearance and behavior of the objects in the universe.
5.3d The energy of a photon is proportional to its frequency.* 5.3e On the atomic
level, energy and matter exhibit the characteristics of both waves and particles.