PHIL215 Lecture : Module 6 - Eternal health and safety issue.docx

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whitejellyfish187

14 Apr 2012

School

University of Waterloo

Department

Philosophy

Course

PHIL215

Professor

Brian Orend

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Document Summary

Module 6 - eternal health and safety issue. It"s not just about pollution that is the health and safety issue, it"s also about product safety (some products physically damage people) Jan narveson"s libertarian critique of environmentalism: convinced that there is no environmental problem at all, vocal minority group out to feather their own nests, base problem on dubious science, hysterical socialist agenda. Systematically underestimates human capacity for technological adaptation. Isn"t that what the earth is for: oil and gas companies, tress and reforestation. Where does this hysteria come from? (that if we take and take there will be nothing left and mass catastrophes) John palmer"s critique of environmentalism 2nd reading: resource gets scarce, supply falls, price goes up, new producers are attracted, deforestation is all supply and demand, diminishment of the resource creates incentives to plant more. Environmentalist being critiqued have certain convictions about the rate of resource depletion. Oil is going to run out in 15 years.

Related Questions

An important question to consider when thinking about globalwarming is, "If the ice sheets near the poles melt, how much willthe sea level rise?" This seems like a difficult question, giventhe odd shapes of both the ice sheets and the oceans. But there aresome accurate approximations that allow the answer to be estimatedfairly accurately with reasonably simple calculations.

The critical idea is that both the thickness of the ice sheets andthe amounts of the sea-level rise are extremely small compared tothe radius of the earth. The radius of the earth is about 2/p x 107m -- more than 6000 kilometers. The ice sheet thicknesses we willbe concerned with are single digit miles and the sea level riseswill be in dozens of feet. As a result, in thinking about them, wecan essentially ignore the curvature of the earth. We can imaginepeeling the map of the earth off a globe and flattening it out (bymaking cuts, not by stretching it, so that we preserve the area).Then, both the ice and the sea level rise can be treated as right(not tilted) cylinders (though with funny shaped bases and tops).Since we know that the volume of a right cylinder is the area ofthe base times the height, we can easily estimate all the volumeswe need. A schematic picture of this approximation (with the heightof the ice mass greatly exaggerated -- you couldn't see it if Ididn't) is shown below. The error in these approximations is on theorder of the height of the cylinder considered divided by theradius of the earth; a very small number.
a. Assume that (after flattening the surface of the earth in ourimaginations) the ice sheet to be considered covers an area, A, andhas a thickness, d. The oceans currently cover about 75% of theearth's surface, and note that the surface area of a sphere is 4pr2where r is the radius of the sphere.

Generate an equation that will allow you to calculate h, the heightthe ocean levels will rise due to the melting of a an ice sheet interms of A, d, and r

b. As shown in the combined satellite photo on the right (fromGoogle Earth), Greenland is covered by a sheet of ice. This ice hasbeen measured to have a mean thickness of about 2 km. Recentobservations indicate that this ice sheet is beginning to retreat-- that it is melting at an accelerating rate.

Using the depth of the ice sheet and the scale given on thepicture, estimate how much sea level rise would be produced by themelting of the entire ice sheet lying on Greenland. (Note: You caneasily look this information up on the web. But the goal of thisproblem is in part to develop your estimation skills for thepurpose of building your ability to decide for yourself whether anygiven piece of information you find on the web is reasonable orbogus.)

1. If a car's wheels are replaced with wheels of greater diameter,will the reading of the speedometer change? Explain.

2. Weightlessness in space is known to have harmful effects on thebodies of people in space. To set up inhabitants (people) in space,it has been suggested that rotating cylinders about 10 miles longand 5 miles in diameter be placed in space. The purpose of theirrotation is to simulate gravity for the people so they have weight.Explain how this is possible?
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Please use DragMath to submit the solutions to problems No. 5 and 6of Activity 9A on page 129 of Bendall & Howison.
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1. Why do the string instruments go flat (lower frequencies) andthe wind instruments go sharp (higher frequencies) during aperformance if an orchestra doesn't warm up beforehand?
2. If you were carrying a fish tank filled with water, what willhappen if your walking frequency matches the natural frequency ofthe water in the tank?
Good luck with these questions. I look forward to a heartydiscussion by Friday this week.
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1. Household circuits are always wired so that the electricaldevices are connected in parallel. Why is this so?
2. How are circuit breakers connected in the household circuits(series or parallel)? What is the use of a circuit breaker? Why isit more advantageous to use a circuit breaker compared to using afuse?
Hope to hear your answers soon.
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Mathematical Question:
Try the question on capacitors Activity 14C no. 3. You can useDragmath to submit your solution. If you are scanning your answersand uploading a file, please keep its size small.
Challenge Question:
A fully charged parallel-plate capacitor remains connected to abattery while you slide a dielectric between the plates. Do thefollowing quantities increase, decrease, or stay the same? (a)capacitance, C (b) charge, Q (c) electric field, E between theplates, (d) change in voltage, V (e) energy stored in thecapacitor.
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Twisted wires: In electrical circuits, it is often the case thatinsulated wires carrying currents in opposite directions aretwisted together. What is the advantage in doing this?
Have a go; looking forward to some interesting replies.
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Metal detectors in airports: When you walk through the doorway ofan airport metal detector, you are really walking through a coil ofmany turns, i.e. an inductor connected to a resonant circuit tunedto the resonant frequency when there is no metal in the inductor.So how does this circuit detect any metal that is in your pocketwhen you walk through the metal detector?
Looking forward to your replies.
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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

PHIL215 Lecture : Module 6 - Eternal health and safety issue.docx

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