# I need a 2nd opinion on a circuit analysis answer

1. Feb 1, 2007

### Number2Pencil

1. The problem statement, all variables and given/known data
Use superposition to find $$I_L$$

2. Relevant equations
-The overall current is the sum of the currents supplied by each source individually

3. The attempt at a solution

for source B only (current source is open):

---ohm's law: $$\frac{100V}{15k + j25k} = 3.43mA( -59.04 degrees)$$

Here is where I'm having to defend my answer:

for souce A only (voltage source shorted):

---since there is no phase shift labeled, it should be assumed that the current source can be treated as a DC source, treating the inductor as a short, making $$I_L$$ -20mA

Is this wrong? Should I treat a current source as AC if it has other AC sources involved in the circuit? If this is so I'd just do a current divider to get $$I_L$$

2. Feb 1, 2007

### doodle

I believe the question would have to be more explicit in defining whether the 20mA is an ac or dc source.

3. Feb 1, 2007

### Number2Pencil

Well no extra information was given than what's shown, yet I got it marked wrong for treating it one way over the other...

Am I going to have to call out my professor again? I'm losing all my brownie points because of his dud test questions

4. Feb 1, 2007

### Gokul43201

Staff Emeritus
I would imagine the "+" by the current source tells you it's a dc source.

5. Feb 1, 2007

### Number2Pencil

Well actually he graded it as it being an AC source.

6. Feb 1, 2007

### doodle

If you are answering the question as part of a test and if the professor is not available to clarify, then I guess you could always offer both solutions, one for each case.

Failing that, then I suppose at the last resort you should treat it as ac since, as you said, there are other ac sources in the circuit.

7. Feb 1, 2007

### doodle

Hmm... but a "+" sign also appears beside the dependent voltage source and that one is clearly ac.

8. Feb 1, 2007

### Gokul43201

Staff Emeritus
Haha! Yes, it does. What on earth is it for, then?

9. Feb 1, 2007

### doodle

For the dependent voltage source, I would imagine that it is there to indicate where the +terminal is (neccesary in defining voltage). I don't know why it appears beside the current source.