Talk:EGR 224/Spring 2009

Typographical / Other Errors

Lab 1

• Below the circuit drawing on p. 2, the statement about the number of equations should be:

 There are four elements and three nodes, meaning a total of 4 element equations, 
 2 independent KCL equations, and (4-3+1)=2 independent KVL equations.

• In Section 1.3, the circuit's voltage source is labeled using the active sign convention not the passive sign convention as recommended in the lab manual. The equations are correctly written for the circuit, however, and the active sign convention is allowed to be used for sources.

Homework

Homework 1

1.14

• You should assume Passive Sign Convention. DukeEgr93 16:21, 11 January 2009 (EST)

1.20

• This question regards current controlled voltage sources. How do you find the voltage across one? Consider problem 1.20 in A&S. The source is labeled 5I₀ with a current of 3 A passing through it. I thought the voltage is just 5*3=15 V, but using Kirchhoff's Voltage Law the voltage definitely should be 10 V. How do you utilize "5I₀" to find the voltage? Thanks! Brs16 12:24, 10 January 2009 (EST)
  • For the circuit in 1.20, the current controlled voltage source (CCVS) has an element equation that says the voltage drop is equal to \(5 I_0\) - the key here is to notice that \(I_0\) is the current through the 28 V element at the top of the circuit; it is listed as being 2 A. Given that, the CCVS has a voltage drop of 10 V, which can be verified with KVL. DukeEgr93 12:10, 11 January 2009 (EST)

Homework 2

3.10

• Once you get the equations symbolically, you can solve and subs using Maple. You probably do not want to do this by hand. DukeEgr93 20:38, 17 January 2009 (EST)

Homework 3

3.38

• How do the mesh currents relate to the 4 A source?
  • Assuming you have drawn the mesh currents clockwise, \(i_1\) measures the current flowing clockwise through mesh 1; its component through the source flows from top to bottom; alternately, \(i_2\) measures the current flowing clockwise through mesh 2 and so its component is going from bottom to top of that source. All of which means \(i_2\) is in the same direction as the source and \(i_1\) is in the opposite direction, so \(i_{source} = i_{2} - i_{1}\) DukeEgr93 17:59, 29 January 2009 (EST)

Homework 6

14.102

• Over which element are we taking the cutoff frequency? For example, in part (a) the circuit is reduced to a simple RC circuit. To find the transfer function, we need to have a V_output, right? —Preceding unsigned comment added by njg6 (talk • contribs)
  • Turns out "which element" will not matter... If you reduce it to two elements, then the half-power frequency will be the same for each. DukeEgr93 18:26, 28 February 2009 (EST)

Homework 8

16.60

• What should the value of the capacitor above the voltage source be? The circuit diagram shows 0.5 \(\Omega\)F. I'm assuming it's supposed to be \(\mu\)F like the other capacitor? MoZ 14:28, 8 April 2009 (EDT)
  • \(\mu\)F it is! DukeEgr93 15:15, 8 April 2009 (EDT)

Homework 9

I: Required

• For the active filter in the required part of Problem 1, how do we know what components to use? I tried using the band pass filter we did in lecture, but this is not possible since we can only vary the two capacitors but yet are constrained by three specifications (two cutoffs and the gain). Any tips? Brs16 11:58, 11 April 2009 (EDT)
  • Never said you might not need more than one resistor at any given location :-D DukeEgr93 15:24, 11 April 2009 (EDT)

II: Optional 1

• This is a little late, but, the problem asks us to find the differential equation for the inductor current \(i_C\)... so should we find the inductor current, or the current through the capacitor as indicated by the symbol? MoZ 13:42, 16 April 2009 (EDT)
  • At this point, I will accept either. DukeEgr93 15:31, 16 April 2009 (EDT)

General Questions

• In Maple, is there a sophisticated way to change a variable/function defined like so i1 = ... to one defined like i1 := ... (this has come up in using the invlaplace command). Bjg13 01:59, 14 April 2009 (EDT)bjg13
  • Two main ways to do this - you can use the assign command on the equation list with the variable of interest or you can use subs to substitute in those values. I generally

use the latter. Section 1.4.7 of EGR 224 Lab 1 has more info. DukeEgr93 09:28, 14 April 2009 (EDT)