Recent content by Underhill

  1. U

    What is the role of frequency synthesizer stages in a receiver and transmitter?

    I've checked the Internet and this forum, and while I notice the term, "tuning resolution" used in different contexts, I can't find a definition. Can anyone provide a clear and concise definition or explanation?
  2. U

    Stuck on Laplace Transform of Odd Trig Function

    Thanks both of you for your help. I eventually solved it by using a half-angle formula on [cos(t)]^2, and then using a trig product formula on the resulting expression. I got the same answer as HallsofIvy. Thanks again, guys!
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    Stuck on Laplace Transform of Odd Trig Function

    Hey guys! I'm stuck on a Laplace transform. Following is the problematic function: [cos(t)]^3 Seems simple, but I'm having issues doing the Laplace transform on odd trigonometric functions. When I use the half-angle formula, I get this, which I can't seem to solve: 1/2cos(t) +...
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    Understanding the Path of Radio Waves (particularly 900 MHz & 2.4 GHz)

    I'm interested in how to understand exactly how radio waves will propagate in a particular situation. I know that they are absorbed by metal and water, pass through other materials albeit with loss of power, and reflect or bounce off of surfaces as well. How do I know whether a radio wave will...
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    Questions Regarding 2011 AP Microeconomics Exam

    Dbouchard: Great explanation; completely explained 1.f.i. for me. Thanks a lot! Matter Wave: Your first paragraph made sense; thanks for the new information about the change of the MR curve with the implementation of a price ceiling. However, I got lost in your last paragraph...
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    Questions Regarding 2011 AP Microeconomics Exam

    This link (http://www.collegeboard.com/student/testing/ap/economics_micro/samp.html?micro has a list of released Microeconomics AP free-response questions. I have a question concerning the 2011 primary released exam. See the questions here...
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    Finding the Maximum Current in an LC-only Circuit

    Thanks! Problem solved! Answers for three parts are below: (i.) 0.2205 Joules (ii.) 0.2970 Amps (iii.) magnitude of 0.4 Amps/second
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    Finding the Maximum Current in an LC-only Circuit

    So, my answer for part (iii.) is 0.4 A/s, but I'm not sure whether there should be a minus sign in front, because I don't know whether the capacitor is charging or discharging. What should I do?
  9. U

    Finding the Maximum Current in an LC-only Circuit

    Thanks, gneill. I see now. I always thought that the V in 1/2QV referred to the battery voltage, not the capacitor voltage. Thanks! Would you mind explaining when the minus sign due to Lenz's Law is relevant? Do I use it when calculating the time rate of change of the current? -LdI/dt +...
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    Finding the Maximum Current in an LC-only Circuit

    I didn't mean voltage on the capacitor - I meant the voltage source in the circuit. If 1/2QV can be used to calculate energy stored in the capacitor at any point in time BEFORE the switch is flipped in a normal RC circuit, then can't I just transfer that value over if I know the switch was...
  11. U

    Finding the Maximum Current in an LC-only Circuit

    Thanks, gneill. (i.) is easy. The energy stored in a partially charged capacitor is \stackrel{1}{2}QV In our case, we get \stackrel{1}{2}(.105)(9.0) = 0.4725 Joules (ii.) is harder. The total energy we have to work (or play) with is the amount of energy stored in the capacitor at time...
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    Finding the Maximum Current in an LC-only Circuit

    Sorry, this is the 2011 test, E&M
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    Finding the Maximum Current in an LC-only Circuit

    Homework Statement Pages 6 and 7 http://apcentral.collegeboard.com/apc/members/exam/exam_information/2008.html I am struggling with Question (2), Part (b), Sections (ii.) and (iii.) Homework Equations RL circuit with battery: I = V/R(1 - e-Rt/L), Imax=V/R RC circuit with battery: I =...
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    How Do You Calculate a'(3) for a = f + 2g Given Derivative Values?

    Think about it. a = f + 2g really means that a at 3 will equal f at 3 added to twice the value of g at 3. The latter information is given you in your table; just do the addition. But how to calculate the derivative of a? That's where the point of the whole problem comes into play. The...
  15. U

    Find Points on 2x^3 + 2y^3 -9xy = 0 Curve

    2x3 + 2y3 - 9xy = 0 To find the lines tangent to this curve, take the derivative: 6x2 + 6y2\frac{dy}{dx} - 9y - 9x\frac{dy}{dx} = 0 2x2 - 3y = 3x\frac{dy}{dx} - 2y2\frac{dy}{dx} (2x2 - 3y) / (3x - 2y2) = \frac{dy}{dx} It is now merely a matter of setting the denominator equal to...
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