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We want to study the dependency of resistivity relatively to the temperature due to the existence of phonons in pure metals.
Show that at high temperatures the number of phonons in a given q mode is proportional to T.
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Subject: Physics | Topic: Modern Physics | ID: 155307
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$ 1.0 |
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Consider two point masses of equal mass m, situated at
eps+ = (a/0) and eps- = (-a/0)
in the lens plane.
Derive the lens equation for this mass distribution.
(Denote the angular separation of the two point masses by theta o, i.e. a = DLTheta o)
Calculate the magnification and determine the caustic
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Subject: Physics | Topic: Modern Physics | ID: 155577
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$ 5.0 |
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If you have a GM detector with a very thin anode wire and the GM is filled with a standard GM fill gas,
how (and why) would you expect the detector to respond to a gamma-rays?
Now lets say you have gas filled proportional counter with a very thick anode wire filled with P-10 gas,
how (and why) would you expect it to respond to alpha particles? ...MORE
Subject: Physics | Topic: Modern Physics | ID: 155579
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$ 3.0 |
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Given the following data:
Assume 2 pi geometry and a one minute count time for all peaks
peak 1 peak 2 peak 3 unknown peak 1 unknown peak 2
channel number 200 700 900 400 1200
photopeak counts 5000 1330 1000 20000 12000
Known energy (keV) 80 320 420 176 570
intrinsic efficiency (%) 15 4 3 100 100
Find the photopeak energy of unknown peaks one and two.
Assuming that the unknown peaks one and two are emitted by different isotopes each with a yield of 1, what is the total activity present in the sample?
Why is it more scientifically rigorous to carry out the above calculations for unknown peak 1 versus unknown peak 2?
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Subject: Physics | Topic: Modern Physics | ID: 155580
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$ 3 |
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A CsI spectroscopy system records a pulse at the 700th channel out of a possible 1024 channel (ranging from 0-10 volts).
The capacitance of the system is 10 pF and the gain of the PMT operating at 1200 bias voltage has a gain of 10,000.
The amplifier gain is set at 10.
The light collection efficiency is 90% while the photocathode efficiency is 12%.
How much energy was originally deposited in the detector? ...MORE
Subject: Physics | Topic: Modern Physics | ID: 155581
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$ 2.0 |
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A particular counting system has a stable average background rate (measured over a long time) of 50 counts/minute. A decaying radioisotope source was introduced and a 10 minute count showed a total of 1683 counts. After a delay of 24 hr, the 10 minute count was repeated, this time giving a total of 914 counts.
a) What is the half-life of the source?
b) What is the expected standard deviation of the half-life due to the counting statistics?
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Subject: Physics | Topic: Modern Physics | ID: 155582
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$ 4.0 |
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A measurement of possible 137Cs contamination on an air filter is made on a daily basis. The measurement consist of placing the filter on a counting system with an absolute gamma ray counting efficiency of 15% at 662 keV for a period of 30 minutes. A new uncontaminated filter is then substituted in the counting system and another 30 minute background count recorded. The background count averages 100 counts per minute.
a) Where should the critical level Lc be set (in units of counts per 30-min measurement) to declare the positive presence of contamination following the criteria of MDA?
b) Under these conditions find the minimum detectable amount (MDA) of 137Cs on the filter. ...MORE
Subject: Physics | Topic: Modern Physics | ID: 155583
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$ 3.0 |
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In space, the radiation field is very different than it is on Earth. On Earth we primarily measure gamma-rays however in space we are primarily interested in
measuring high energy heavy charged particles. These particles are mostly hydrogen and helium with some trace amounts heavier nuclei. Their energies range from hundreds of MeV to hundreds of GeV.
Discuss how each of the three classes of detectors (gas filled, scintillators, and solid state detectors) may or may not be used to perform spectroscopy on these heavy charged particles. ...MORE
Subject: Physics | Topic: Modern Physics | ID: 155584
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$ 3.0 |
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1. Give all possible decays of W+ and Zr0 boson to fermion-antifermion pair.
2. The particle g(4S) has the mass 10.579 GeV/c2. It is produced in the collision of a positron and an electron. The energy of the positron is 3.100 GeV.
What is the minimal energy of electron required to produce this particle? ...MORE
Subject: Physics | Topic: Modern Physics | ID: 155638
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$ 2.0 |
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A pi° meson with mass M(pi°) = 0.135 GeV/c2 decays to two photons: pi° —> gg. The angle between the direction of one photon and the x-axis in the centre of mass frame of the pi° meson is 60° degrees. The pi° meson has a momentum of 10.00 GeV/c in the laboratory frame directed along the x-axis.
What is the energy of the second photon in the laboratory frame? ...MORE
Subject: Physics | Topic: Modern Physics | ID: 155639
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$ 2.0 |
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The mean proper lifetime of B+ meson is 1.67 x 10-12 s, and its mass is 5.279 GeV/c2. The energy of B+ meson in the laboratory frame is 20.000 GeV.
a) B+ meson decays at the distance 3.00 millimeters from the production point in the laboratory frame.
Find its lifetime in the rest frame of B+ meson.
b) Find the probability that the distance between the production and decay points of B+ meson exceeds 5.00 millimeters in the laboratory frame.
c) What type of detector is required to measure its lifetime?
...MORE
Subject: Physics | Topic: Modern Physics | ID: 155640
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$ 2.0 |
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Charged pi+ meson with mass 140 MeV/c2 and momentum p =1.000 GeV/c passes through the detector consisting of two parallel planes of silicon, see the picture. Each plane is 400 /µm thick. The initial direction of the pi+ meson is perpendicular to the first plane. The distance between two planes is 3.0000 cm. The radiation length of silicon is 9.3600 cm.
a) Give the distribution of the angle t1 of direction of the pi+ meson after passing the first plane (see the picture), and find the RMS of this distribution.
b) Find the RMS of distribution of distance y2 of the point A to the initial trajectory of the pi+ meson. The point A corresponds to the position of the pi+ meson when it enters into the second plane (see the picture).
Assume that there is no multiple scattering m the air between the planes.
c) Find the RMS of distribution of angle t2 of direction of the pi+ meson after passing both planes.
Assume that there is no multiple scattering in the air between the planes.
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Subject: Physics | Topic: Modern Physics | ID: 155642
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$ 3.0 |
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A hydrogen atom at rest in its first excited state emits a photon and ends up in the ground state
a. How much momentum does the photon carry off?
b. How much kinetic energy does the hydrogen atom acquire?
Does this energy need to be taken into account in determining the energy of the emitted photon?
Why or why not?
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Subject: Physics | Topic: Modern Physics | ID: 155656
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$ 4.0 |
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Anyone who has studied quantum mechanics has seen the Heisenburg uncertainty principle, which is frequently written as (Δx)(Δp) ≥h
What precisely does this statement mean?
(to answer this question, you will want to define each quantity or symbol in this relation carefully, and you might want to consider implications if any, for such things as making measurements on a bubble chamber photograph, tracking the flight of a baseball, or performing a double slit experiment). In other words, what does this fairly abstract equation tell us about the physical world.
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Subject: Physics | Topic: Modern Physics | ID: 155657
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$ 3.0 |
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One triumphs of the early quantum theory was the bohr model of the atom and its application to hydrogen. Today we describe the hydrogen atom by solving the Schrodinger equation.
How are the two descriptions alike?
How do they differ?
Which is better and why?
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Subject: Physics | Topic: Modern Physics | ID: 155658
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$ 2.0 |
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What is a wave function?
In other words, if you have calculated a wave function ?(r,t) for a given potential, what is the meaning of this function?
What does it tell you about physical system in question?
(you might get at this issue by addressing such questions as:
Is the wave function “real”?
Is it a property of the physical system?
Does everyone electron have its own wave function?
Why or why not?
Is the wave function a “complete” description of a physical system?) ...MORE
Subject: Physics | Topic: Modern Physics | ID: 155659
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$ 2.0 |
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What is the Compton Effect?
What are the implications for the Compton Effect for physical theory?
(That is, can you explain the Compton Effect in classical terms? In Quantum Mechanical terms? If so, how; if not, why not?) ...MORE
Subject: Physics | Topic: Modern Physics | ID: 155660
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$ 2.0 |
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What is the photoelectric effect?
How can the photoelectric effect be explained in classical terms (if it can)?
How can it be explained in quantum mechanical terms? ...MORE
Subject: Physics | Topic: Modern Physics | ID: 155661
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$ 2.0 |
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What is blackbody radiation?
How does classical theory explain blackbody radiation?
How does quantum theory? ...MORE
Subject: Physics | Topic: Modern Physics | ID: 155662
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$ 2.0 |
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According to Hund's Rules, what should be the ground state quantum numbers for fluorine?
For silicon?
Are your answers consistent with observations ...MORE
Subject: Physics | Topic: Modern Physics | ID: 155663
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$ 2.0 |
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