Name:________________________
Regents Physics
Date:________
Mr. Morgante
UNIT 6
MODERN PHYSICS &
THE STANDARD
MODEL
Dual Nature of Light and the Photoelectric Effect
Einstein’s photon theory of light brought up a question that most physicists believed had
been answered in the debates between Christian Huygens and Isaac Newton… is light a
particle or a wave? You have discussed light as a wave… always. But now serious
questions had been raised as to whether or not this was true.
Before we decide if light is a wave or particle, let’s examine the properties of the
photoelectric effect based on each.
“Light is a Wave”
To keep one variable a constant, we will assume that we are testing monochromatic light
(one color, one frequency).
· A higher intensity of light (like a brighter bulb) means a higher
amplitude of wave
· A higher amplitude means that the wave has more energy.
· We would expect that if light is a wave, as the intensity of the light
increases more electrons with higher Ek should be ejected.
· The frequency should not affect photoelectric effect, since it has nothing
to do with the energy of the wave.
Example: You’re at the water park at West Edmonton Mall. The wave
machine is going so that it is making small waves (small amplitude). You
could stand up to your waist in the water all day without getting moved,
because the waves just don’t have enough energy to move you. Even if they
increase the frequency of the little waves (so that more hit you every second),
the waves are still too small to push you around. It’s only when they increase
the amplitude (the size of the waves) that you can get pushed off your feet.
You represent the surface electrons on the metal, and the water waves are light
waves.
“Light is a Particle”
We will still assume that we are dealing with monochromatic light, but now we assume
light is a particle (the photons in Einstein’s theory).
·
Since E = h¦, monochromatic light will be made up of photons that all
have the same energy.
·
This is the energy that could eject electrons and give the Ek.
·
The energy of the light will only increase if the frequency of the light
increased.
·
Increasing the intensity of the light only causes more photons of the
same energy to hit the surface, so more electrons would drop off, but they
all have the same maximum kinetic energy.
Example: You are so bored studying physics that you decide to go practice
your forehand in tennis. You go to a court that has one of those automatic ball
machines that shoots balls at you. Unfortunately the wiring is all fried and it
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starts shooting balls at you! Getting hit with one ball every ten seconds isn’t
too bad, but then it cranks up the frequency and hits you with ten balls every
ten seconds… ouch! That hurts! So you run off the court. Even though each
ball was still being shot at you with the same velocity (intensity), they were
hitting you a lot more frequently.
You represent the surface electrons on the metal, and the tennis balls are photons
of light.
Which model is right?
Well, you’ve already seen that Einstein’s use of Planck’s ideas to explain the
photoelectric effect depend heavily on the frequency of light, but is there any other
evidence that supports the particle theory of light?
Millikan performed further experiments with the photoelectric effect in 1913-14 and
found that at any frequency less than the threshold frequency (fo) no electrons are
emitted, no matter how great the intensity of the light. An increase in the intensity of the
light only means more electrons are emitted, but since the energy of each photon hasn’t
changed, the maximum Ek of each electron stays the same.
So, now we have evidence that light behaves as a particle, at least when it comes to
explaining the photoelectric effect. But we still have to recognize that light has some
properties (diffraction, interference) that are better explained using a wave model… so
both models are right! The current model of light is usually referred to as “wave-particle
duality”. We now recognize that light is both a particle and a wave. This means that
sometimes a wave acts like a particle!
Photoelectric Effect
Late in the year 1900, Max Planck (pronounced “Plonk”) came up with a new idea that
might be able to solve the problems everyone was having trying to explain blackbody
radiation.
to be the source of blackbody radiation) could vibrate at any frequency.
any amount of energy.
about radiation acting like a wave and Maxwell’s equations).
Planck tried to figure out a formula that would fit the experimental data, even if he didn’t
have a good theory to back it up.
if he assumed that electrons
could only vibrate at specific frequencies.
energy.
of energy of the electrons vibrating at a frequency…
3
E = hf
E = energy of the radiation (J)
h = Planck’s Constant = 6.63x10 - 34 J∙s
f = frequency of the emitted radiation (Hz)
(or packets of energy called quanta!) You could have 1, 2, 3, …, pieces of radiation,
as long as you had a whole number… no fractions!
o This sounds like Millikan showing that charges always come in multiples of
1.6x10-19C and Thompson showing that electrons always had the same
mass.
o Only now we are taking about Electromagnetic Radiation, including light!
Planck said that energy is not continuous as shown on the graph, but instead lots of very
small points that look like a solid line. This is sort of like when you look at a picture in
the newspaper… looks like a continuous picture, but it’s actually made up of little dots
that blend together. Quantum.
The smallest amount of energy possible at a given frequency (E=hf) is called a
quanta of energy. This just means a “piece” of energy.
Quanta – singular
Quantum – plural
The value for Planck’s Constant (h = 6.63 x 10 -34Js) is a universal constant, just like the
gravitational constant, G.
Example: What is least amount of energy from a light source that emits at a
frequency of 4.50 x 1014 Hz?
E = hf
= (6.63 x 10 -34Js)(4.50 x 1014 Hz)
E = 2.98 x 10 –19 J
Einstein Investigates Photoelectric Effect
At the beginning of the 1900’s Albert Einstein linked Hertz’ research on the photoelectric
effect to the work of Planck.
·
Remember, Planck said that an object emits energy according to the formula
E = hf.
·
Einstein said that when an object emits light, the object must decrease its
energy by that same amount… E= hf.
·
So light must be released in “packets” of energy…
·
Wait a second… he saying light is emitted as tiny particles, not waves…
·
He called these packets of light “photons”
To test his theory, Einstein examined the photoelectric effect.
A device similar to this one was set up:
4
Einstein ran several different tests with this apparatus.
1. What happens when the voltage source is turned off and the device is in
the dark (no UV radiation falls on the plate)?
Nothing happens. There are no readings on the ammeter, which is exactly
what we would expect. As shown above, this is a broken circuit that (at the
moment) has no voltage source.
2.
What happens when the voltage source is turned off and the device is
exposed to radiation with a frequency less than UV?
Again, nothing happens. This agrees with the original experiment that
Hertz performed, since he found that you need frequencies of radiation
that were equal or greater than UV before anything happens at the metal
plate.
3.
What happens when the voltage source is turned off and the device is
exposed to radiation with a frequency equal to or greater than UV?
Now a current is shown by the ammeter readings! Einstein hypothesized
that there were electrons being “ripped” off of the metal plate (as Hertz
had observed). Einstein believed that these electrons then moved towards
the electrode and hit it, which completes the circuit. This is why a current
is shown on the ammeter.
4.
What happens if the voltage source is turned on, and slowly increased?
Notice that the variable voltage source is set up so that the electrode will
be negative and the metal plate becomes positive. This voltage should
work against the electrons getting all the way from the metal plate to the
electrode. Only electrons with sufficient kinetic energy (going fast
enough) will be able to get to the electrode.
The voltage was slowly increased from zero, and for a while nothing
appeared to be changing. But, there came a point when the voltage became
too great for electrons to get across the gap. At this point (and for any
higher voltages) the ammeter gives a reading of zero.
5
Work Function
Einstein believed that to give a single electron this energy to move, a single photon hit
the metal surface (destroying itself), and transferred its energy to the one electron.
·
Since the electron is attracted to the surface of the metal, some minimum
amount of energy must be needed just to snap it off. Otherwise, electrons
would just be dropping off of atoms all the time.
·
Einstein called this the work function of the material, since you needed to
do work on the electron to break it off.
·
Since yanking the electrons started to happen at a minimum frequency
(usually around UV), he called it the
W = work function (J or eV)
threshold frequency of the material.
h = Planck’s constant
·
This was all related to Planck’s
formula E=hf in the following way…
f0= threshold frequency (Hz)
W = hf0
The work function of materials goes as high as about 10eV.
Example: What is threshold frequency of a material with a work function of
10eV
Since the value for the work function is given in electron volts, we might as
well use the value for Planck’s constant that is in eV s.
W = h o
o = W / h
= (10eV) / (4.14 x 10-15eVs)
o = 4.14 x 10-14 Hz
Photoelectric Effect Formula
·
If the frequency of the incoming light is great enough, there should be
enough energy to break off the electron and have some left over to give it
some kinetic energy. So…
hf = Ek max + W
·
·
·
Which just basically says, if a photon (E=hf) transfers its energy to an
electron, the electron has energy to tear away from its surface (W) and energy
to move (Ek)
This follows the conservation of energy, since the photon’s original energy
is equal to the energy it takes to snap off the electron and get it moving.
Note: some electrons will need more than the bare minimum W to be
released (they might be attracted more strongly), so their Ek is not as great as
the maximum.
·
That’s ok, though, since we’ll only worry about the electrons that came
off the easiest and have the maximum kinetic energy.
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Example: The work function of silver is 4.73eV. Electromagnetic Radiation with
a wavelength of 1.20x1015Hz strikes a piece of pure silver. What is the speed of
the electrons that are emitted?
To figure out the answer you will need to go through a few steps…
Calculate the maximum Ek first…
hf = Ek + W
Ek = hf – W
= (4.14x10-15eVs)(1.20x1015Hz)
– 4.73eV
Ek = 0.238 eV = 3.81 x 10-20J
Then calculate the speed of the
electron…
Ek = ½ mv2
v = 2.89 x 105m/s
Notice that in this example I used the value for Planck’s constant that is given
in eVs, rather than Js. This saved me the trouble of changing the work
function into Joules. But, it is just as important to realize that this results in an
answer in eV which I have to change into Joules before I can use the kinetic
energy formula. If you are more comfortable always working with standard
units, go for it! If you changed the work function for silver into Joules you’d
be doing great. In fact, if you’re ever in doubt, change everything into
standard units and go from there. Because eV are so common in this unit.
Compton & deBroglie
Einstein
For a while Einstein continued research into the photoelectric effect.
 He showed (using the photoelectric effect) that even though light had no mass, it
still had kinetic energy.
 Einstein predicted that we showed see another particle characteristic in light
waves… momentum!
 Based on his findings he predicted that photons have momentum which could be
calculated by the formulas…
and
…but at the time he had no way of confirming that these formulas were true.
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Compton Effect
In 1923 A.H. Compton started shooting
high frequency x-rays at various
materials.
 Found that the x-rays
scattered after hitting the
target (graphite worked really
well to cause this effect).
 The radiation that was
scattered after hitting the
graphite had a slightly longer
wavelength than the incident
x-ray.
Remember, longer wavelength = smaller frequency.
 Since E = h, the scattered photons had less energy!


He then found that electrons were being thrown off the target.
Compton was able to explain all he was seeing (which became known as the
Compton Effect) by using the photon theory of light…
 As incident photons collided with the electrons, they transferred some
of their energy to them
 He applied the conservation of momentum and energy to the
experiment, and found the results agreed!
 Photons obey the laws of conservation of momentum and energy!
 This provided support of Einstein’s theories that EM radiation has
momentum.
deBroglie Wavelengths
In 1923 Prince Louis de Broglie proposed a new idea…
 Could things believed to be particles (like electrons and baseballs) sometimes
act like waves?
 All the stuff discovered so far has shown that electromagnetic radiation
sometimes acts like a particle, so deBroglie just wanted to know if particles
could act like waves.

de Broglie said that since
then it should be easy to substitute p = mv
into the formula…


This is the de Broglie Wavelength of a Particle.
8


Nobody really took de Broglie seriously until Einstein read his paper and
agreed with his ideas.
Now the hard part… finding experimental data to support the theory.
 The problem was that no one had ever seen a particle diffract or interfere
with another particle, which would be proof that the particle was acting
like a wave.
 Notice that the wavelength of everyday objects would be very small.
Example: What is the de Broglie wavelength of a 0.20kg ball moving at 15m/s?

Remember from Young’s Double Slit experiment that to be able to see the effects
of diffraction and measure wavelength, you need slits or objects which are not
much larger than the wavelengths being studied.
 It is impossible to build a diffraction grating as small as 10-34m! So for large
objects we have a problem.
 But notice where mass is in the formula… with a really small mass (like an
electron), the wavelength gets bigger!

Although this is very small, the spaces between the atoms of a crystal are about
this size.
 Davisson and Germer shot electrons at a metal crystal and observed a
diffraction pattern.
 The conclusion: Particles have wave properties!
So, the wave-particle duality applies to objects as well as light.
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EINSTEIN’S E=mc2
MAIN POINTS:
 EINSTEIN DISCOVERED THIS THEORY IN 1905.
 THE THEORY RELATES THE MASS OF AN OBJECT TO THE
AMOUNT OF ENERGY THAT OBJECT CONTAINS. IN OTHER
WORDS, MASS AND ENERGY ARE THE SAME, THEY ARE JUST IN
DIFFERENT FORMS.
 THIS STATEMENT IN EQUATION FORM IS E=mc2. UNITS ARE FOR
E ARE JOULES (J), m IS MASS IN kg, c IS THE SPEED OF LIGHT IN A
VACUUM (3x108 m/s).
 THIS THEORY IS GOVERNED BY THE LAWS OF CONSERVATION
OF MASS AND ENERGY.
 A SMALL AMOUNT OF MASS CAN PRODUCE IMMENSE POWER,
THIS IS THE BASIS FOR NUCLEAR ENERGY AND NUCLEAR
WEAPONS.
EX. PROB 1:
a) 1 kg OF MASS IS CONVERTED INTO HOW MUCH ENERGY?
KNOWNS: m=1kg; c=3x108 m/s (FROM REF. TABLE)
UNKNOWN: E
E=m c2 E=(1kg)*( 3x108 m/s)2 = 9x1016 joules
b) HOW MANY MeV IS THIS EQUAL TO?
1Ev = 1.6x10-19 J (FROM REF. TABLE)
9x1016 joules x 1Ev/1.6x10-19 J = 5.625x1035 eV = _________ MeV
c) HOW MANY UNIVERSAL MASS UNITS IS THIS EQUAL TO?
START W/ REF. TABLE FOR CONVERSION, SHOW ALL WORK.
Alpha decay happens in elements further down the periodic table because the strong
nuclear forces in the atom are not able to hold a very large nucleus together.
daughter nucleus plus the alpha particle is less than the mass of the original
parent nucleus.
following Einstein’s famous formula E = mc2.
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Example: How much energy is released when Uranium-238 decays to Thorium234
This is an alpha decay. The reaction for it would be…
It is possible to look up the total masses of these atoms in text books. They
would be…
There’s 0.0046u unaccounted for after the reaction has occurred. Since 1u
= 931.5MeV, the energy released in this reaction is 4.3MeV. This energy
is found (mostly) in the kinetic energy of the alpha particle and daughter
nucleus moving away from each other.
Fusion
Nuclear fusion can result when atoms or subatomic particles combine.
Example: Proton + Neutron
Mass of p+ = 1.00782 amu
Mass of n0 = 1.00866 amu
Mass of
= 2.01410 amu
Add them up and you’ll find the total mass on the left is more than the total mass on the
right!
This mass didn’t disappear, it was turned into energy according to Einstein’s formula E =
mc2 .
In the above example the difference in mass (called the “mass defect”) is…
2.01410 – (1.00782 + 1.00866) = 0.00238 amu
= 3.95 x 10-30 kg
The energy released would be…
E = mc2
= 3.95 x 10-30 kg (3.00 x 108 m/s)2
E = 3.56 x 10-13 J
This may not seem like a lot of energy, but remember that it came from the
fusion of just one proton and neutron. If we could trillions of these reactions
going every second the release of energy would be impressive!
Also, notice what the product is… not highly radioactive elements like in a
fission reaction… here we get good old hydrogen!
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So why don’t we use fusion instead of fission?
 Unfortunately at this stage in our technology we haven’t worked out all the bugs
yet.
 We can build and run fusion reactors right now, but we end up putting in more
energy than we get out.
o Fusion reactions require intense heat and pressure to allow fusion to
happen.
 There is a great deal of research working on “cold fusion”, the ability to cause
fusion to happen at lower temperatures.
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What is Particle Physics?
Particle physics is the study of what everything is made of. Particle Physicists study the
fundamental particles that make up all of matter, and how they interact with each other.
Everything around us is made up of these fundamental building blocks of nature. So,
what are these building blocks?
In the early 1900's it was believed that atoms were
fundamental; they were thought to be the smallest
part of nature and were not made up of anything
smaller.
Soon thereafter, experiments were done to see if this
truly was the case. It was discovered that atoms were
not fundamental at all, but were made up of two
components: a positively charged nucleus surrounded
by a cloud of negative electrons.
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Then the nucleus was probed to see if it was fundamental,
but it too was discovered to be made up of something
smaller; positive protons and neutral neutrons bound
together with the cloud of electrons still surrounding it.
Now that these protons and neutrons were found, it was time to see if they were
fundamental. It was discovered that they were made up of smaller particles called
"quarks", which today are believed to be truly fundamental, along with electrons.
Furthermore, electrons belong to a family of fundamental particles, which are called
"leptons". Quarks and leptons, along with the forces that allow them to interact, are
arranged in a nice neat theory named The Standard Model.
The Standard Model
The Standard Model is a theoretical picture that describes how the different elementary
particles are organized and how they interact with each other along with the different
forces. The elementary particles are split up into two families, namely the quarks and the
leptons. Both of these families consist of six particles, split into three generations, with
the first generation being the lightest, and the third the heaviest. Furthermore, there are
four different force carrying particles, which lead to the interactions between particles.
The table below shows this all a little bit more clearly.
14
So, is everything in the world made up of quarks and leptons? Well, not quite. Next stop,
Antimatter.
What is Antimatter?
An interesting thing that has been discovered about matter particles, is that each one has a
corresponding antiparticle. The term "anti" may be a bit deceiving, as it is still real
matter. The only difference between a particle and its antiparticle is that an antiparticle
has the opposite electrical charge.
15
Think of it as a mirror image. In our experience left
and right are the only things to reverse when looking
in the mirror. Similarly, in the particle world, charge
is what reverses when looking in the "mirror". It's
mass, spin, and most (quarks have something called
colour charge which is also changed in the "mirror")
other properties are the same.
In general, an antiparticle is the particles name with "anti" in front of it. For example, the
antiparticle of the proton is the antiproton. An exception to this rule is the electron, whose
antiparticle is known as the positron.
An interesting fact about antimatter is that the entire universe is made up of matter as
opposed to antimatter. This is somewhat of a mystery.
On to Quarks.
What are Quarks?
To start with, there are six types of quarks (plus their six antiquarks), which are coupled
into three pairs. They are the up-down, the charm-strange, and the top-bottom (sometimes
known as truth-beauty). Another interesting fact about quarks is that you can never find
one by itself, as they are always with other quarks arranged to form a composite particle.
The name for these composite particles is "hadrons". Quarks, like protons and electrons,
have electric charge. However, their electric charges are fractional charges, either 2/3 or 1/3 (-2/3 and 1/3 for antiquarks), and they always arrange to form particles with an
integer charge (i.e. -1, 0, 1, 2...).
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Flavour
Mass
(GeV/c2)
Electric Charge
(e)
u
up
0.004
+2/3
d
down
0.08
-1/3
c
charm
1.5
+2/3
s
strange
0.15
-1/3
t
top
176
+2/3
b
bottom
4.7
-1/3
Because quarks join with each other to form particles with integer charge, not every kind
of combination of quarks is possible. There are two basic types of hadrons. They are
baryons, which are composed of three quarks, and mesons, which are made up of a quark
and an antiquark. Two examples of a baryon are the neutron and the proton.
The proton is composed of two up quarks and one down quark.
As you can see, when the charges from the individual quarks are
added up, you arrive at the familiar charge of +1 for the proton.
The neutron is made up of two down quarks and one up quark.
Again, adding the charges from the quarks up, we arrive at
zero.
17
An example of a meson is the pion. It is composed of an up quark and
a down antiquark. Because mesons are a combination of particle and
antiparticle, they tend to be very unstable and decay very quickly.
So we've now talked about quarks, but there is still the other family of elementary
particles to talk about, the "leptons", which we will now discuss.
What are Leptons?
Like quarks, there are six types of leptons, and again, in three pairs. Electron - neutrino,
muon - neutrino, and tau - neutrino (these three neutrino's are different from each other).
The electron, muon, and tau each carry a negative charge, whereas the three neutrinos
carry no charge. Leptons, unlike quarks, exist by themselves, and, like all particles, have
a corresponding antiparticle.
Flavour
Mass
(GeV/c2)
Electric Charge
(e)
electron neutrino
<7 x 10-9
0
electron
0.000511
-1
muon neutrino
<0.0003
0
muon
(mu-minus)
0.106
-1
tau neutrino
<0.03
0
tau
(tau-minus)
1.7771
-1
As the chart indicates, the tau and muon are much heavier than the electron. Furthermore,
they are not found in everyday matter. This is because they decay very quickly, usually
into lighter leptons. There are a couple of rules that govern the decay of leptons.
Rule One: One decay product of a heavy lepton will always be its corresponding
neutrino. The other products could be a quark and its antiquark, or a lighter lepton and its
antineutrino.
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Rule Two: The total number of family members before and after must be conserved
(realizing that an antiparticle is considered a negative family member). For example, if a
tau particle decays into a lighter lepton, the tau's corresponding neutrino will be a product
of the decay, keeping a total of 1 family member before and after the decay. The other
products could be a lighter lepton and its corresponding ANTIneutrino, keeping a total of
zero members before and after for that family of leptons. This is because:
Let's now go on to the next topic, the Forces Of Nature.
The Forces of Nature
There are four fundamental forces in nature.
1. Electromagnetism
2. Strong
3. Weak
4. Gravity
These four forces all occur because of the exchange of force carrier particles. Don't
understand?
Well, pretend you want to knock a bird out of a tree 100
yards away. You must exert a force to do this, but the
darn bird is out of your reach. So, you take out a pitching
wedge and a golf ball, take a swing. If you're good
enough, you will successfully exert a force on the bird
and knock it down from its perch, with the golf ball being
the force carrier.
Not all types of matter though are affected by all force carrying particles. For example,
the proton and electron are affected by the force carrier particle of the electromagnetic
force, the photon. They can emit and absorb photons. The neutrino on the other hand, is a
mass particle without charge, and is thus not affected by the photon and will not emit or
absorb one.
First stop, Electromagnetism
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Electromagnetism
Electromagnetism is one of the two forces that dominate our everyday lives (the other
one being gravity). The words you are reading radiating from your monitor are a result of
electromagnetism, and so is the force that your chair exerts on your body to keep you
from falling to the ground (and to the center of the Earth.) The electromagnetic force acts
between all particles that have electric charge. It is attractive for oppositely charged
particles, and repulsive for particles of the same charge.
The electromagnetic force gets weaker and weaker the further apart the particles are, but
it's range is infinite. The carrier of this force is the photon, most commonly observed as
light.
Another thing the electromagnetic force is responsible for is binding atoms together to
form molecules. Although most atoms have a net neutral charge, the positive charge from
within one atom can attract a negative charge within another atom, thus binding the two
atoms together. This is called the "residual electromagnetic force".
The next force we will look at is the strong force.
The Strong Force
In addition to electric charge, quarks also contain something called "colour charge". The
force between colour charged particles is very powerful, thus it is called the "strong
force".
The strong force is strictly an attractive force, which acts between nucleons (protons and
neutrons). It attracts any combination of protons and neutrons. i.e. neutrons attract
neutrons, protons attract neutrons... This is the force that overcomes the repulsive force
within an atom due to the electromagnetic force and holds the nucleus together.
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The strong force actually acts between quarks, and it's the
residual strong force (similar to the residual
electromagnetic force) that causes nucleons to attract.
The carrier of this force is the gluon.
The next force we'll look at is The Weak Force.
The Weak Force
All the stable matter in the universe appears to be made up of one type of lepton (the
electron) and two quarks (the up and down), which compose the neutron and the proton.
However, there have been six types of each that have been predicted and observed,
The reason why we don't observe these more
massive quarks and leptons is due to the weak
force. It is the weak force that causes massive
leptons and quarks to decay into lighter
leptons and quarks.
The force carriers that lead to these decays are the W+ and W- particles, which both have
an electrical charge, and the neutral Z particle.
One more force to go, Gravity
Gravity
Gravity acts between all particles that have mass. Mass will attract other mass with a
force that gets weaker as the distance between them gets larger. Gravity is responsible for
the large scale structure of the universe. Here's a pretty picture of a galaxy, which, of
course, is held together by gravity.
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Although gravity appears to be a very powerful force, when it comes to things on smaller
scales, like tiny particles, can be ignored because of its weakness. The carrier of the
gravitational force is the gravitron. Although it has never been observed in experiment, it
is strongly believed to exist.
PARTICLE INTERACTION SUMMARY TABLE
INTERACTION
FORCE
RELATIVE
STRENGTH
RANGE OF
FORCE
FIELD PARTICLE THAT
AFFECTS THE FORCE
STRONG
1
SHORT
GLUON
ELECTROMAGNETIC
10-2
LONG ( 1/r2)
PHOTON
WEAK
10-6
SHORT
W & Z BOSONS
GRAVITATIONAL
10-43
LONG ( 1/r2)
GRAVITON
EXAMPLES:
YOU WILL BE RESPONSIBLE FOR KNOWING THE QUARK COMBINATIONS
FOR A PROTON, NEUTRON AND ANTIPROTON. WE KNOW THAT YOU NEED
3 QUARKS TO FORM A BARYON, WHICH IS WHAT PROTONS, NEUTRONS &
ANTIPROTONS ARE. WE ALSO KNOW THE CHARGE OF A BARYON SUCH AS
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A PROTON IS +1, THEREFORE THE ELECTRIC CHARGE OF AN ANTIPROTON
MUST BE –1.
THE QUARK COMBINATION OF A PROTON IS THEREFORE UP, UP, DOWN, OR
uud WHILE THE QUARK COMBINATION OF A NEUTRON IS DOWN, DOWN UP
OR ddu. AN ANTIPROTONS COMBINATION IS ANTI-UP, ANTI-UP, ANTIDOWN. REMEMBER, YOU MUST PUT BARS ABOVE THE LETTERS FOR THE
ANTIPROTON; uud.
23
Name____________________
Regents Physics
Date:___________
Mr. Morgante
Modern Physics Notesheet
Wave Particle Duality of Energy & Matter:
1. List below how waves of electromagnetic energy are identified (think about the
electromagnetic spectrum on your Reference Table):
a. ______________
b. ______________
c. ______________
d. ______________
2. What other phenomena do electromagnetic waves exhibit:
a. ______________
b. ______________
c. ______________
Waves Have a Particle Nature:
3. What other phenomena does light display when it interacts with matter?
__________________________________________________________________
__________________________________________________________________
4. Give an example of what can happen when light strikes matter.
__________________________________________________________________
__________________________________________________________________
5. The phenomenon called that was discussed it item 4. above is called the
__________________________________.
Quantum Theory:
Define the following:
6. Quantum Theory (look up discrete if you don’t know what it means):
__________________________________________________________________
__________________________________________________________________
7. Quantum:__________________________________________________________
8. The amount of ______________ of each _______________ is directly
proportional to the _________________ of the electromagnetic radiation.
a. The equation for the energy of a quantum is ___________________.
24
b. What is the value of Planck’s constant (h) __________________. This is
an empirical number, what does that mean?
9. The basic unit of quantum is called a ________________________.
10. A photon is a ______________ particle of light. It carries both ___________ &
______________.
Equation
Variables/ constants
Units
Can be used to find
Vector/scalar
h
h
h
f
f
f
c
c
c
λ
λ
λ
f
f
f
h
h
h
c
c
c
λ
λ
λ
E = hf
c =λ f
E= hf =hc/ λ
Graph practice:
E = hf , E versus f
versus f
E
E = hc/ λ , E versus λ
c =λ f , v constant, λ
λ
E
f
λ
f
Algebra practice:
a. Assume speed of light in a vacuum is constant:
a. Calculate wavelength of 20 Hz light
b. Calculate wavelength of 20 kHz light
a.____________________
b.____________________
b. Assume speed of light in a vacuum is constant:
a. Calculate wavelength of red light
b. Calculate wavelength of violet light
a.____________________
b.____________________
25
Photon Particle Collisions:
Photoelectric Effect: When a photon(s) is incident (a.k.a. hits) a metal surface, the surface
absorbs the energy to a certain threshold and then emits the absorbed energy via an
electron.
11. What happens when X-ray photons strike a metal surface?
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
Sketchies:Copy and label the review book sketches for the following phenomena:
Collision of an X-ray photon and an electron in an atom:
12. The incident photon loses _____________ & ___________________.
13. If the photon loses energy, then the frequency of the photon _________________.
14. The electron gains ______________ & __________________.
15. If the electron gains energy, then the frequency of the photon ________________.
16. The momentum of a photon depends on ______________ OR ______________.
Particles Have a Wave Nature:
17. Matter & radiation have both ___________ & _____________characteristics.
18. _________________ & _______________ phenomena provide evidence for the
wave nature of particles.
Early Models of the Atom:
19. Define Atom:
__________________________________________________________________
__________________________________________________________________
26
Thomson’s Model:
20. Electron’s are low ______________, ________________ charged particles.
21. Atoms are electrically __________________, therefore the number of
___________ and __________ must be equal in order to have a balance of
charge.
Rutherford’s Model:
Using internet research, draw a diagram below of Rutherford’s Model:
Rutherford’s Model
22. A beam of massive positively charged particles (called alpha particles which are
nuclei of helium atoms) were shot at a gold foil. Rutherford discovered that most
of the alpha particles went directly _________ the gold foil.
23. Some of the alpha particles ____________ back.
24. Some of the alpha particles ______________ to the side.
25. The experiment showed that most of the mass of an atom is in its
_____________. This region of the atom is __________________ charged.
Bohr Model of the Hydrogen Atom:
Explains how electrons don’t collide into the nucleus (b/c positive & negative charges
attract).
26. All forms of energy are _____________________. Redefine quantized:
_____________________________________________________________________
_____________________________________________________________________
27. The electron in the hydrogen atom can only occupy certain ______________ of
fixed _______________.
28. Electrons can jump orbits by ____________ __________________ of energy in
the form of a _________________.
29. Each orbit corresponds to a ____________ amount of ____________.
27
29a. Closer the electron is to the nucleus, the _________ energy it has (think
about potential energy from electrostatics b/c it applies here).
Energy Levels:
30. Define excitation:
____________________________________________________________________.
31. Excitation occurs when an object absorbs _______________ due to the collision
of ______________ or ______________________________.
32. Energy here also has to be absorbed in _____________ of energy.
33. Atoms want to return to the ___________ state after they absorb energy. They
then release this ________ in the form of ___________ of specific
______________.
34. Define a spectral line
_____________________________________________________________________
_____________________________________________________________________
Ionization Potential:
35. Define Ionization Potential:
__________________________________________________________________
__________________________________________________________________
36. Draw the energy level diagram below for a Hydrogen Atom (note the Level and
corresponding energy in electron volts):
37. What is the limitation of the Bohr
Model?___________________________________________________________
__________________________________________________________________
28
The Cloud Model:
38. Electrons are not _____________ to specific ____________. Electrons here are
spread out everywhere, but are found the most where the regions are
______________ because this is where you would have the highest probability of
electrons.
Atomic Spectra:
39. Define Atomic Spectra:
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
40. Each element has its own_____________________________ that differs from
every other element.
Emission (Bright Line) Spectra:
-When an excited electron in an atom comes back to the ground state, the emitted photon
energy is equal to the following equation:
Ephoton = Ei – Ef
41. Where Ei is the _____________________________________________
42. Where Ef is the _____________________________________________
43. What do we use a spectroscope for?
_____________________________________________________________________
_____________________________________________________________________
44. Define Emission Spectrum/Bright Line Spectrum:
_____________________________________________________________________
_____________________________________________________________________
Absorption Spectra:
Define Absorption Spectrum:
_______________________
_______________________
_______________________
_______________________
_______________________
_______________________
Sketch Abs. Spectra in the box
How does Absorption Spectum
Differ from Emmision Spectrum?
___________________________
___________________________
29
Name:__________________________
Date:______________
Regents Physics
Mr. Morgante
The Standard Model Notesheet
The Nucleus:
1. Protons and neutrons that make up the nucleus of an atom are called
_____________________.
Nuclear Force:
2. Protons in the nucleus are separated from each other by very small distances. The
order of magnitude of this separation is ___________ meter.
3. The large repulsive _____________ force wants to separate them while the
_______________ force wants to try and attract them but his force is too weak in
comparison.
4. It is therefore the ______________ force that keeps the protons together in the
nucleus.
5. The __________ force is about __________ times stronger than the ___________
force.
6. The _____________ force only works at extremely small distances.
Universal Mass Unit:
7. Define the universal mass
unit:______________________________________________________________
__________________________________________________________________
8. Notation for a universal mass unit is _________.
9. The universal mass unit of a proton is _____________________ as found on
Reference Tables.
10. The universal mass unit of a neutron is _____________________ as found on
Reference Tables.
11. The universal mass unit of an electron is _____________________ as found on
Reference Tables.
12. 1 universal mass unit = ________________ kg. (This is on the Ref. tables also!)
30
Mass-Energy Relationship:
13. This is also known as Einstein’s most famous discovery. The equation is
__________________.
14. E stands for _____________ and the units are ____________. m stands for
__________ and the units are__________. c stands for the _____________ of
_________ and the units are __________.
15. We can also express E in terms of the units ________________. The conversion
from _____________ to _____________ can be found on the front sheet of the
reference tables.
16. This theory states that we can take a certain _____________ and convert it to
________________.
Nuclear Mass and Energy:
17. The mass-energy relationship is __________________ at all levels from
___________ to __________.
18. The total mass of two protons and neutrons is 2 x (_____________ +
_______________). The mass of a helium-4 nucleus is 4.0016 u. Therefore, the
mass of the _________________ is less than the addition of the individual
protons and neutrons. This is true for all _______________ except
________________.
19. In order to break up the nucleus, we must overcome the _______________ force,
therefore _____________ must be done.
Studying Atomic Nuclei:
20. A particle accelerator uses ___________ and ___________ fields to project
_____________ & _____________ at speeds near the __________ of
___________.
21. Collisions between these particles disrupt the ____________ and __________
new particles. The study of the _______________ particles provide information
about the ______________ and ___________ within the ____________.
The Standard Model of Particle Physics:
22. The Standard Model of Particle Physics is the process by which scientists have
begun to build a ___________ of the structure of a _____________.
31
The Fundamental Forces in Nature:
23. In modern physics, scientists refer to particles as _____________ carriers because
of the exchange of particles.
24. The four fundamental forces are ___________________,
_____________________, ___________________, __________________.
25. The weak force is a __________ range force that is responsible for the
_________________ of some _____________ particles such as alpha particles,
gamma rays, etc.
Classification of Particles:
26. Particles can be classified according to the ____________ of _______________
they have with other _______________.
27. A hadron is either a _____________ or _____________. It interacts through the
___________ force, the ____________ force and the weak ___________ and the
____________ force.
28. A lepton is either a ______________, a positron, or a ________________. They
interact by the _________________, __________________, ______________
forces.
29. A __________ has a mass less than that of a _____________.
30. A _______________is a _____________ whose mass is equal to an
_____________, but it has a __________ charge instead of an electron which has
a _______________ charge.
31. A _______________ is a particle with little or no __________, but it has
___________ & ___________.
You can see all of these items below in the Reference Table.
32. A ______________ is a particle that can be ______________ into a
________________ or _____________. It is also known as a ______________
particle.
33. A _________ is a particle of _____________ mass. This just means that its mass
is what makes it different than a baryon.
34. An _______________ is a particle having the same characteristics (mass, half
life, spin [ because these particles spin like little planets]) of the ___________
associated particle but with ___________ charge. If you place a _________ over
the symbol of a particle it is now denoted as an antiparticle.
32
35. A proton symbol is __________. An antiproton symbol is ___________.
36. _______________ is material consisting of _________________ that are
composed of _________________, _____________________,
____________________.
The Quark:
37. The ________________ and _______________ are composed of smaller
___________ called _______________.
38. The charge on a quark is either ___________, or __________. Remember from
electrostatics that 1e is the charge on a proton. Therefore, you have to add quarks
to make up a proton of 1e.
39. Quarks are named ___________, ___________, _____________,
_______________, ________________, ________________. They can be seen
on the Reference Tables.
40. Every ___________ is a combination of _________ quarks and every meson is
made up of __________ & ___________.
41. An _______________ is the ____________ of a quark. Again we are just
changing the _____________ of the original particle.
42. A proton must add up to a charge of +1e therefore a combination of an ____,
____, _____ quark combination would work. A neutron would have to add up to
0e, therefore a ____, ____, _____ quark combination would work. The same
thought process works for mesons.
33
NAME________________________________
Regents Physics
DATE________
Mr. Morgante
Modern Physics Worksheet
______1. The energy of a photon is inversely proportional to its
(1) wavelength
(2) speed
(3) frequency (4) phase
______2. The energy equivalent of the rest mass of an electron is approximately
(1) 5.1 x 105 J
(2) 8.2 x 10-14 J
(3) 2.7 x 10-22 J (4) 8.5 x 10-28 J
______3.Which combination of quarks could produce a neutral baryon?
(1) c d t
(2) c t s
(3) c d b
(4) c d u
______4. A photon of light carries
(1) energy, but not momentum
(3) both energy and momentum
(2) momentum, but not energy
(4) neither energy nor momentum
______5. The force that holds protons and neutrons together in the nucleus is known as
the
(1) gravitational force (2) strong force (3) magnetic force (4) electrostatic force
______6. Protons and neutrons are examples of
(1) positrons
(2) baryons (3) mesons
(4) quarks
______7. If a deuterium nucleus has a mass of 1.53 x 10-3 universal mass units (u) less
than its components, this mass represents an energy of
(1) 1.38 MeV
(2) 1.42 MeV (3) 1.53 MeV (4) 3.16 MeV
______8. Excited hydrogen atoms are all in the n = 3 state. How many different photon
energies could possibly be emitted as these atoms return to ground state?
(1) 1
(2) 2
(3) 3
(4) 4
______9. A baryon may have a charge of
(1) - 1/3 e
(2) 0 e
(3) + 2/3 e
(4) + 4/3 e
______10. Which force between the proton and neutrons in a tritium atom (31H) has the
greatest magnitude?
(1) electrostatic force (2)gravitational force (3) magnetic force (4) nuclear force
34
Name:____________________
Regents Physics
Date:_________
Mr. Morgante
Modern Physics Free Response #2
Base your answers to questions 1 through 4 on the information below.
When an electron in an excited hydrogen atom falls from a higher to a lower energy
level, a photon having a wavelength of 6.58 x 10–7 meter is emitted.
1.
Calculate the energy of a photon of this light wave in joules. [Show all
calculations, including the equation and substitution with units.] [2]
2.
Convert the energy of the photon to electronvolts. [1]
3. Determine which two energy levels the electron has fallen between to emit this
photon. [1]
4.
Is this photon an x-ray photon? Justify your answer. [1]
35
Base your answers to questions 5 through 7 on the passage below and on your
knowledge of physics.
Forces of Nature
Our understanding of the fundamental forces has evolved along with our growing
knowledge of the particles of matter. Many everyday phenomena seemed to be governed
by a long list of unique forces. Observations identified the gravitational, electric, and
magnetic forces as distinct. A large step toward simplification came in the mid-19th
century with Maxwell’s unification of the electric and magnetic forces into a single
electromagnetic force. Fifty years later came the recognition that the electromagnetic
force also governed atoms. By the late 1800s, all commonly observed phenomena could
be understood with only the electromagnetic and gravitational forces.
~Particle Physics–Perspectives and
Opportunities (adapted)
A hydrogen atom, consisting of an electron in orbit about a proton, has an approximate
radius of 10–10 meter.
5
Determine the order of magnitude of the electrostatic force between the electron
and the proton.[1]
6
Determine the order of magnitude of the gravitational force between the electron
and the proton.[1]
36
7
In the above passage there is an apparent contradiction. The author stated that “the
electromagnetic force also governed atoms.” He concluded with “all commonly
observed phenomena could be understood with only the electromagnetic and
gravitational forces.”
Use your responses to questions 6 and 7 to explain why the gravitational
interaction is negligible for the hydrogen atom. [2]
Base your answers to questions 8 and 9 on the diagram below, which shows some energy
levels for an atom of an unknown substance.
37
8
Determine the minimum energy necessary for an electron to change from the B
energy level to the F energy level.
9
Calculate the frequency of the photon emitted when an electron in this atom
changes from the F energy level to the B energy level. [Show all work, including the
equation and substitution with units.]
38
Name:____________________
Regents Physics
Date:_________
Mr. Morgante
Modern Physics Worksheet #3
1.
A baryon may have a charge of
(1) -1/3e
(2) 0 e
(3) +2/3e
(4) +4/3e
2. A metal surface emits photoelectrons when illuminated by green light.This
surface must also emit photoelectrons when illuminated by
(1 ) Blue light
(3) Orange light
(2) Yellow light
(4) Red light
3. When an electron changes from a higher energy state to a lower energy within an
atom, a quantum of energy is
(1 ) fissioned
(3 ) emitted
(2 ) fused
(4 ) absorbed
Base your answers to questions 4 and 5 on the diagrams below, which show a photon and
an electron before and after their collision.
4
Compared to the wavelength of the photon before its collision with the electron,
the wavelength of the photon after the collision is
(1) shorter
(2) longer
(3) the same
5
Compared to the total momentum of the photon-electron system before the
collision, the total momentum of the photon-electron system after the collision is
(1) less
(2) greater
(3) the same
Before Collision
After Collision
Incident
High-energy Photon Electron in an Atom
Electron
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