# Circuit with switch.

Discussion in 'Homework Help' started by cdummie, Sep 18, 2015.

1. ### cdummie Thread Starter Member

Feb 6, 2015
104
1
When the switch in the circuit is closed, then I=(3-j)A. Find complex power of Ig1 when the switch is off if we know that then, complex power of Ig2 is Sig2=(10+j6)VA.

Known values are: Z=(2-j2)Ohms , Z1=(1+j2)Ohms, Z2=Z4=(2+j4)Ohms, Z3=(2-j4)Ohms, Ig1=(0.5+j1.5)A and E=(7+j3.5)V.

In the first case, there's no impedance Z in the circuit, does it means that there's no Ig2 in the circuit since both ends of Ig2 are on the same potential or i'm wrong, i am not really sure about this because that would mean that Ig2 is zero and how then it's complex power can be (10+j6)VA?

RRITESH KAKKAR likes this.
2. ### WBahn Moderator

Mar 31, 2012
18,085
4,917

Ig2 is a constant current source. By definition, whatever current it put out yesterday it is putting out today and it will put out tomorrow.

3. ### cdummie Thread Starter Member

Feb 6, 2015
104
1
So how should i approach this, any hints?

4. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,500
511
Mesh-Current Method or Node-Voltage Method, you pick one.

5. ### cdummie Thread Starter Member

Feb 6, 2015
104
1
I though about that, but i don't know the values of E2, E3 and Ig2.

6. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,500
511
You know power at Ig2 when switch is Off. So you can probably figure out Ig2.

E2 and E3... yeah, I would need to get some equations going to figure out if finding their values is possible.
I notice that you are not doing it, therefore I don't see any reason why I should.

7. ### cdummie Thread Starter Member

Feb 6, 2015
104
1
I understand, but i think that this could be solved using theorems, doing it with methods could take way too much time and it could be useless, so i thought about theorems, but i couldn't figure out which one would be good. Anyway, i will try to use the power of Ig2 somehow in second case, as you mentioned, so thanks for advice.

8. ### Russmax Member

Sep 3, 2015
81
12
This is a methods problem, not a theorems problem. You have to do a fair amount of algebra here.