# Circuits problems

Discussion in 'Homework Help' started by kirit, Oct 31, 2008.

1. ### kirit Thread Starter Active Member

Sep 9, 2008
35
0
Hello, I seem to be in need of some help with some homework problems. Cant seem to pinpoint why Im having so much trouble getting them done correctly. I'll post them one at a time so any help given will be easier to discuss. Thanks in advance!!!!!

So looks like an easy problem, not sure why I keep having to bang my head against a wall to get it right. I get an answer that is very close to that. I get 2^.5 * cos(40t - 135), so instead of +135 i get -135.
Here is my work:

Hope the pics are clear. If not I can type the work up. Thanks for the help again.

Feb 4, 2008
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3. ### kirit Thread Starter Active Member

Sep 9, 2008
35
0
Thats part of me banging my head against the wall. I did and rechecked my signs. I even did it the first time using nodal analysis but couldnt get the answer.

4. ### Ratch New Member

Mar 20, 2007
1,068
3
kirit,

It appears you are right and the book is wrong. See the attached file. Interestingly, V1 appears to be zero.

Ratch

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5. ### The Electrician AAC Fanatic!

Oct 9, 2007
2,255
311
This is an interesting circuit. For purposes of discussion, eliminate Vs and number the nodes across the top of the circuit, left to right, V1, V2 and V3. The frequency for all calculations will be w=40.

Typically in a circuit with an unsymmetrically placed dependent source, the circuit is non-bilateral; for example, the equivalent circuit of a 3 terminal amplifying device such as a vacuum tube or a transistor.

But this one appears to be still bilateral.

The voltage transfer ratio (VTR; also known as voltage gain or loss) from from V1 to V3 (apply a voltage source to V1 and calculate V3/V1) is just unity. The VTR from V1 to V2 is zero.

Interestingly, the VTR from V3 to V1 is also unity, and from V3 to V2 is also zero.

But now, for those who wish to exercise their circuit analysis skills, try these:

Calculate the VTR from V2 to both V1 and V3.

Calculate the current transfer ratio (CTR; also known as current gain or loss), from V1 to V3. This is done by applying a current source to V1 and shorting V3 to ground. The CTR is the current in the short at V3 divided by the current applied to the input, V1; in other words, I3/I1, with a short at node V3.

Calculate the CTR from V3 to V1. Is the network bilateral for CTR?

Calculate the impedance from V1 to V3 as though measured by a floating AC impedance meter (at a frequency of w=40).

Calculate the impedance from V1 to V3 with the 2 ohm resistor removed.

6. ### Ratch New Member

Mar 20, 2007
1,068
3
The coil forms a series resonant circuit with the capacitors on each side of it. That is why the voltage on the high side of the resistor is the same as ground or zero, and the output voltage is the same as the input voltage. If Vs is removed, then no "i" is present, so the dependent current source outputs zero amps, and Vo is zero also.

Ratch