PHL376H1 Lecture : January 31 Lecture Notes

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orangejellyfish260

8 Feb 2012

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Cheating is best identified with the intentional violation of a public system of rules to secure the goals of that system for oneself or for those about whom one is concerned. Is the ethics of sport simply expressive of the values of the wider society or do the principles of sport have a degree of independence from those social values. Externalism about the ethics of sport is the view that sport is not a fundamental source of ethical principles or values. Externalism & the overemphasis on winning (e. g. , nhl shootouts: neo-marxist account, play theorist account, radical feminist account. On each account given by hundley, the overemphasis on winning occurs because sport simply expresses (and so perpetuates) the values of wider society (such as winning). A man finds himself engaged in an athletic contest in which victory is very important to him.

Related Questions

Consider a system consisting of N noninteracting atoms in asubstance at temperature T and volume V placed in an externalmagnetic field B pointing in the z direction. The magnetic energyof an atom can be taken as
e=-ÂµiB
where Âµ is the magnetic moment of the atom. In this problem, wewill not consider the detailed contributions to the atomic magneticmoment from both the orbital and electron spin angular momentum;rather we will take the atomic magnetic moment to simply be givenby
Âµ=-gÂµBJ/?? in terms of the atomic g-factor, Bohr magneton, and thetotal angular momentum of the atom.

(a) Write the energy per atom noting that the magnetic field is inthe z direction. (b) Given that the magnitude and z component ofthe total angular momentum are
quantized, write the energy per atom in terms of the magneticquantum number mj , indicatingtherangeoftheallowedmjvaluesintermsofj,thequantumnumber associated with the magnitude ofthe total angular momentum. (For electron spin, j = 1/2 and mj = Â±1/2.)
(c) How many values of mj are there?

In a circuit containing only resistors, the basic (though notnecessarily explicit) assumption is that the current reaches itssteady-state value instantly. This is not the case for a circuitcontaining inductors. Due to a fundamental property of an inductorto mitigate any "externally imposed" change in current, the currentin such a circuit changes gradually when a switch is closed oropened.
Consider a series circuit containing a resistor of resistance andan inductor of inductance connected to a source of emf andnegligible internal resistance. The wires (including the ones thatmake up the inductor) are also assumed to have negligibleresistance.
Let us start by analyzing the process that takes place after switchis closed (switch remains open). In our further analysis, lowercaseletters will denote the instantaneous values of various quantities,whereas capital letters will denote the maximum values of therespective quantities.
Note that at any time during the process, Kirchhoff's loop ruleholds and is, indeed, helpful:
.
Part A
Immediately after the switch is closed, what is the current in thecircuit?
Hint A.1
How to approach the problem
Hint not displayed
ANSWER:

zero
Answer not displayed
Part B
Immediately after the switch is closed, what is the voltage acrossthe resistor?
Hint B.1
Ohm's law
Hint not displayed
ANSWER:

zero
Answer not displayed
Part C
Immediately after the switch is closed, what is the voltage acrossthe inductor?
Hint C.1
A formula for voltage across an inductor
Hint not displayed
ANSWER:

zero
Answer not displayed
Part D
Shortly after the switch is closed, what is the direction of thecurrent in the circuit?
ANSWER:
clockwise
counterclockwise
There is no current because the inductor does not allow the currentto increase from its initial zero value.
Answer not displayed
Part E
Shortly after the switch is closed, what is the direction of theinduced EMF in the inductor?
ANSWER:
clockwise
counterclockwise
There is no induced EMF because the initial value of the current iszero.
Answer not displayed
Part F
Eventually, the process approaches a steady state. What is thecurrent in the circuit in the steady state?
ANSWER:

Answer not displayed
Part G
What is the voltage across the inductor in the steady state?
Hint G.1
Induced EMF and current
Hint not displayed
ANSWER:
zero

Answer not displayed
Part H
What is the voltage across the resistor in the steady state?
ANSWER:
zero

Answer not displayed
Part I
Now that we have a feel for the state of the circuit in its steadystate, let us obtain the expression for the current in the circuitas a function of time. Note that we can use the loop rule (goingaround counterclockwise):
.
Note as well that and . Using these equations, we can get, aftersome rearranging of the variables and making the subsitution,
.
Integrating both sides of this equation yields
.
Use this last expression to obtain an expression for . Rememberthat and that .
Express your answer in terms of , , and . You may or may not needall these variables. Use the notation exp(x) for .
ANSWER:
=
Answer not displayed
Part J
Just as in the case of R-C circuits, the steady state here is neveractually reached: The exponential functions approach their limitsasymptotically as . However, it usually does not take very long forthe value of to get very close to its presumed limiting value. Thenext several questions illustrate this point.
Note that the quantity has dimensions of time and is called thetime constant (you may recall similar terminology applied to R-Ccircuits). The time constant is often denoted by . Using , one canwrite the expression

as
.
Find the ratio of the current at time to the maximum current.
Express your answer numerically, using three significantfigures.
ANSWER:
=
Answer not displayed
Part K
Find the time it takes the current to reach 99.999% of its maximumvalue.
Express your answer numerically, in units of . Use threesignificant figures.
ANSWER:
=
Answer not displayed

Part L
Find the time it takes the current to reach 99.999% of its maximumvalue. Assume that ohms and millihenrys.
Express your answer in seconds, using three significantfigures.
ANSWER:
=
Answer not displayed
seconds
Part M
Find the time it takes the current to reach 99.999% of its maximumvalue. Assume that ohms and henrys.
Express your answer in seconds, using three significantfigures.
ANSWER:
=
Answer not displayed
seconds
Part N
What fraction of the maximum value will be reached by the currentone minute after the switch is closed? Again, assume that ohms andhenrys.
Use three significant figures in your answer.
ANSWER:
=
Answer not displayed
Now consider a different situation. After switch has been closedfor a long time, it is opened; simultaneously, switch is closed, asshown in the figure. This effectively removes the battery from thecircuit.
The questions below refer to the time immediately after switch isopened and switch is closed.
Part O
What is the direction of the current in the circuit?
ANSWER:
clockwise
counterclockwise
The current is zero because there is no EMF in the circuit.
Answer not displayed
Part P
What is happening to the magnitude of the current?
ANSWER:
The current is increasing.
The current is decreasing.
The current remains constant.
Answer not displayed
Part Q
What is the direction of the EMF in the inductor?
ANSWER:
clockwise
counterclockwise
The EMF is zero because the current is zero.
The EMF is zero because the current is constant.
Answer not displayed
Part R
Which end of the inductor has higher voltage (i.e., to which end ofthe inductor should the positive terminal of a voltmeter beconnected in order to yield a positive reading)?
Hint R.1
How to approach the problem
Hint not displayed
ANSWER:
left
right
The potentials of both ends are the same.
The answer depends on the magnitude of the time constant.
Answer not displayed
Part S
For this circuit, Kirchhoff's loop rule gives
.
Note that , since the current is decreasing. Use this equation toobtain an expression for .
Hint S.1
Initial and final conditions
Hint not displayed
Hint S.2
Let us cheat a bit
Hint not displayed
Express your answer in terms of , , and . Use exp(x) for .
ANSWER:
=
Answer not displayed

1. The Yukawa Potential energy function for the interaction ofneutrons and protons in a nucleus is . (a) What is the forceassociated with this potential energy? (b) If and Find the value ofthe force at r=a and at r=3a

2. For what value of the constant c is the forceconservative?

3. In a two-stage rocket, the exhaust velocity for the first stageburn is 3000 m/s and for the second stage burn is 3000 m/s. Assumethat during the entire sequence of burns the rocket is still nearenough to the surface of the earth to approximate the externalgravitational acceleration as 9.8m/s^2 , and ignore air resistance.The mass of the first stage engine and tanks is 2000kg. The mass ofthe fuel held in the first stage is 4000kg. The first stage fuelburns in 10 seconds. The first stage is then ejected. The mass ofthe second stage engine, tanks, and payload is 2000kg. The mass ofthe fuel held in the second stage is 2000kg. The second stage fuelburns in 5 seconds. (The second stage tanks remain attached to thepayload when empty.) (a) At what speed is the second stage/payloadcombination moving at the end of the second stage burn? (b) Howmuch faster is this than the speed if all the 6000kg fuel wereburned in the first stage in 15 seconds with the same exhaustvelocity (3000m/s) and the entire 4000kg assembly of the emptyrocket remained in one piece?

4. A particle with mass 10kg starts from rest at r = 10 and ?=0radians, following the trajectory given by r=10-2t , ?=0.2t. Findthe radial and angular components and of the force, as functions oftime, that will cause this motion

5. A sheet of material, mass 2kg, uniform density, is in the shapeof a right triangle bounded by the lines y=0, x=0, and y=4-x. Itattched to the origin, and free to rotate about the y axis. A forceof 1000 Newtons is applied perpendicular to the plane, located atthe x=4 point on the triangle as it starts to rotate. In aright-handed coordinate system, how fast will the object bespinning (in radians per second) as it crosses the y-z plane (thatis, when it has rotated through 270 degrees)?

Thank you in advanced.

PHL376H1 Lecture : January 31 Lecture Notes

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