Solving Parallel Circuits with Dependent Sources Using Ohm's Law | Homework Help

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In summary, the conversation is discussing a problem involving a dependent source and parallel resistors. The solution involves finding the voltage drop across the 2kohm resistor and accounting for the polarity of v1 in order to get the correct answer of -2V.
  • #1
-EquinoX-
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Homework Statement



http://img96.imageshack.us/img96/4527/wrongs.jpg [Broken]

Homework Equations





The Attempt at a Solution



so I found that:

6 = 2000i + 2000i
6 = 4000i
i = 3/2000

V0 = 3/2000 * 2000
= 3

so therefore the dependent source is 1 mA

and then combining both parallel resistors together I got: 4/3 k ohm

so V = 4000/3 ohm * 0.001 A

is this right??

the answer doesn't seem to match anything
 
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  • #2
You are close. Treat the right loop as if the current is only going through 2kohm resistor. You do have an open loop, so no current will flow through the 4kohm resistor. What then can you say about the voltage drop across the 2kohm resistor?
 
  • #3
so is it 2V?

well the answer key says it's -2V, I don't understand why
 
  • #4
It would be 2V if the voltage v1 was flipped (positive at the top and negative at the bottom). You got your voltage drop across the 2kohm resistor to be 2V (positive at the top and negative at the bottom) which is right, but because the polarity is opposite of v1 we need to account for that. We can flip the polarity by negating the value of the voltage. That is why it is -2V. It would be the same if they showed V0 with an opposite polarity. You would record it as -3V if they had the polarity opposite to what they have now.
 
  • #5
I thought if the current was the opposite of the voltage then it's negative, and here the current is the same direction as voltage...
 
  • #6
You are right about the voltage and current directions. But here you are not finding the voltage across the 2kohm resistor, you are finding v1. Try placing v1, the polarity and all, on the 2kohm resistor (without changing the current direction) then record the voltage according to the voltage/current reference direction rule.EDIT: Sorry if I am of not much help. Anyone please feel free to jump in.
 
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  • #7
thanks, that totally helps out!
 

1. How do I use Ohm's Law to solve parallel circuits with dependent sources?

To use Ohm's Law in solving parallel circuits with dependent sources, you need to first identify the dependent sources in the circuit. Then, you can use the equations V = IR and I = V/R to solve for the unknown voltages or currents at each node in the circuit.

2. What are dependent sources in a parallel circuit?

Dependent sources are voltage or current sources whose values are dependent on other parameters in the circuit. For example, a dependent voltage source's value may be determined by the current flowing through a resistor, while a dependent current source's value may be determined by the voltage across a diode.

3. Can I use Kirchhoff's Laws to solve parallel circuits with dependent sources?

Yes, Kirchhoff's Laws can still be used to solve parallel circuits with dependent sources. However, Ohm's Law may be more helpful in finding specific values at each node in the circuit.

4. What are some common mistakes when solving parallel circuits with dependent sources?

Some common mistakes include forgetting to account for the dependent source in the calculations, using the wrong equations for dependent sources (e.g. using V = IR for a dependent current source), and not properly simplifying the circuit before solving.

5. Are there any shortcuts for solving parallel circuits with dependent sources?

Yes, there are a few shortcuts that can make solving parallel circuits with dependent sources easier. One is to redraw the circuit with the dependent sources removed and replace them with equivalent circuits using known values. Another is to use nodal analysis to find the voltage at each node, and then use Ohm's Law to solve for the currents.

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