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Course Overview
Relativity
•  The speed of light is the same for ALL
observers, even if they are moving toward or
away from the source of light
•  Nothing travels faster than light
and
Practical Consequences:
GPS, Magnetism, Snell’s Law, Doppler Effect,
Nuclear Binding Energy, E=mc2
Use your clicker to decide
The Theory of Relativity…..
A.  Only applies in outer space
B.  Only applies to things moving close to
the speed of light
C.  Is needed to understand cars driving
along the highway
D.  Has few if any practical applications
E.  None of the above
Light as a Wave
If Light is an electromagnetic wave, lets start by looking at
how waves behave.
Ocean Waves
entering a Cove
•  Where the long ocean waves enter the opening of the cove,
they spread out in rings, as if from a point.
•  This phenomenon is called Diffraction
• Exactly the same thing happens to sound, and EM waves
(light, radio, X-rays etc)
24.1 Huygens’ Principle and Diffraction
Large aperture
Small aperture
The smaller the aperture (or the more the waves are
disturbed) the less information remains about the
original direction of the waves.
Interference Pattern
Airey Pattern: Diffraction by a circular aperture
For a circular hole (for example your eye’s pupil, or the
aperture in a camera) the diffraction pattern is a central
maximum, surrounded by concentric rings
The angular diameter of the
central spot (in radians) is
θmin = 1.22λ/D
Where D is the diameter of
the aperture (in meters)
•  This fact is a fundamental limitation for ALL optical devices
•  Nothing smaller than θmin can be resolved, no matter what the
magnification!
ConcepTest 24.5a
The diffraction pattern below arises
from a single slit. If we would like
to sharpen the pattern, i.e., make
the central bright spot narrower,
what should we do to the slit width?
Diffraction I
1) narrow the slit
2) widen the slit
3) enlarge the screen
4) close off the slit
ConcepTest 24.5a
The diffraction pattern below arises
from a single slit. If we would like
to sharpen the pattern, i.e., make
the central bright spot narrower,
what should we do to the slit width?
Diffraction I
1) narrow the slit
2) widen the slit
3) enlarge the screen
4) close off the slit
The angle at which one finds the first
minimum is:
sin θ = λ / d
The central bright spot can be
narrowed by having a smaller angle.
This in turn is accomplished by
widening the slit.
d
θ
θ
Why can’t we see bacteria without a microscope?
Why can’t you recognize people a mile away?
What is the smallest detail on the Earth’s surface that can be made out in
photos taken by a camera with a 2.3m diameter objective mirror, carried by
on a satellite in near earth orbit?
The Hubble Space Telescope (diameter 2.3 m is similar to the imaging satellites flown
by the National Reconnaissance Office (NRO), except they look DOWN!
Mirrors and Lenses
Electromagnetism
•  Magnetic Fields are caused by what?
A. 
B. 
C. 
D. 
Magnetic Charges
Electric Fields
Electric Currents
Charges in Motion
•  Faraday’s Electromagnetic lab, computer simulation in
mastering physics.
•  Check your understanding of practical applications for the exam.
(resistance, capacitance, power, energy lost in wires,
transformers, work done by electric fields…etc.)
Electric Generators - Wind Turbine
Generators that use magnets and coils, plus a
source of mechanical power are often called
Alternators - there’s one in your car!
Alternators are the simplest and most efficient
type of generator.
They produce alternating current.
Coils
Magnets
If an object is heated, it
will start to glow. Which
of, the following is true?
A.  A glowing red object is hotter than a glowing yellow
object
B.  A glowing blue object is hotter than a glowing red object
C.  Very hot objects glow mainly in the infrared
At what wavelengths does your body radiate the most electromagnetic
energy?
A.  Around 9000-10000 nm
B.  At exactly 9354.8 nm
C.  Around 300-700 nm
D.  I don’t radiate
electromagnetic waves
because my body isn’t
magnetic
Energy Levels in the Atom
Which of the following
transitions will cause the
atom the radiate light of
the shortest wavelength?
A.  n=4 to n=1
B.  n=3 to n=2
C.  n=4 to n=3
D.  n=1 to n=2
ConcepTest 27.1
Which has more energy, a
photon of:
Photons
1) red light
2) yellow light
3) green light
4) blue light
5) all have the same energy
400 nm
500 nm
600 nm
700 nm
ConcepTest 27.1
Which has more energy, a
photon of:
Photons
1) red light
2) yellow light
3) green light
E = hf
400 nm
4) blue light
5) all have the same energy
500 nm
600 nm
700 nm
The photon with the highest frequency has the most energy
because E = hf = hc/λ (recall that c = f λ). So a higher
frequency corresponds to a lower wavelength. The highest
energy of the above choices is blue.
What’s “wrong” with this diagram of the photoelectric
effect?
A.  Red light cannot eject
electrons because it
carries too little energy
B.  Two photons are shown
hitting the surface but 3
electrons are being
ejected
C.  Nothing is wrong, as long
as the photons carry
enough energy they can
eject any number of
electrons
Most Nuclear Radiation is Natural
Fun facts:
•  The most radioactive thing most of us encounter in a year is a banana.
•  Your radiation dose from flying in a plane is greater than your dose from the security X-ray scanner at check-in.
ConcepTest 31.6 Radiation Shielding
Which type of radiation goes
1) alpha radiation
farther in matter before
2) beta radiation
losing all of its energy ?
3) gamma radiation
4) all about the same distance
ConcepTest 31.6 Radiation Shielding
Which type of radiation goes
1) alpha radiation
farther in matter before
2) beta radiation
losing all of its energy ?
3) gamma radiation
4) all about the same distance
Alpha particles have such a large
charge, they ionize many atoms in
α
a short distance, and so lose their
β
energy rapidly and stop. Gamma
γ
rays travel great distances before
ionizing an atom.
paper aluminum
lead
Types of High energy Radiation
• Why do these different
radiation types have such
different penetrating
abilities?
• What other types of
experiments would
distinguish them?
• How would you measure
their mass and charge, if
any?
30.3 Radioactivity
Alpha and beta rays are bent in opposite directions in a
magnetic field, while gamma rays are not bent at all.
Remember the Right Hand Rule
ConcepTest 30.4b Particle Emission II
A radioactive substance decays
and the emitted particle passes
through a uniform magnetic field
pointing into the page as shown.
In which direction are gamma rays
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
deflected?
source
×
×
×
×
B field
ConcepTest 30.4b Particle Emission II
A radioactive substance decays
and the emitted particle passes
through a uniform magnetic field
pointing into the page as shown.
In which direction are gamma rays
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
deflected?
source
Gamma rays are uncharged,
so they will not be deflected
by a magnetic field.
Follow-up: What particles are bent to the right?
×
×
×
×
B field
Cloud Chamber
photographs
Above: Ionization tracks made
by high energy particles.
Right: The addition of a
magnetic field causes the
particles to form curved,
circular, or even spiral tracks.
Nuclear Binding Energy
To compare how tightly bound different nuclei are, we
divide the binding energy by A to get the binding
energy per nucleon.
• Rapid estimates of total
binding energy for any
element can be made
from this graph
• Compare binding
energy of reactants and
products to find the
energy released (or
required)
• Energetics of Fission
and Fusion reactions
• Stability of Nuclei
• Practical calculations
for Nuclear power
ConcepTest 30.2c Binding Energy III
On a balance scale, you put
2 neutrons and 1 proton on
one side and you put a
tritium nucleus (3H) on the
other. Which side weighs
more?
1) the 2 neutrons and 1 proton
2) the tritium nucleus
3) they both weigh the same
4) it depends on the specific
isotope of tritium
ConcepTest 30.2c Binding Energy III
On a balance scale, you put
2 neutrons and 1 proton on
one side and you put a
tritium nucleus (3H) on the
other. Which side weighs
more?
1) the 2 neutrons and 1 proton
2) the tritium nucleus
3) they both weigh the same
4) it depends on the specific
isotope of tritium
need to add 8.5 MeV
to balance scale
The mass of the 2 neutrons and
1 proton is less when they are
bound together as tritium. The
mass difference is the binding
energy.
30.11 Radio-Carbon Dating
•  Radioactive dating can be done by analyzing the fraction of carbon in
organic material that is carbon-14.
•  The ratio of carbon-14 to carbon-12 in the atmosphere has been roughly
constant over thousands of years. A living plant or tree will be constantly
exchanging carbon with the atmosphere, and will have the same carbon
ratio in its tissues.
•  When the plant dies, this exchange stops. Carbon-14 has a half-life of
about 5730 years; it gradually decays away and becomes a smaller and
smaller fraction of the total carbon in the plant tissue.
•  This fraction can be measured, and the age of the tissue deduced.
Use of Polarizer to remove Reflections and Glare in
Photography (and Everyday life)
Without polarizer:
(or adjusted horizontally)
Reflections in surface of water
With Polarizer:
(adjusted vertically)
Reflections suppressed.
The leaves at the bottom of the
pond are now visible