Parallel Circuit with current source and dependent current source. HELP!

I've deleted your other thread. It doesn't matter how you're learning, I'm sure what you want is assistance, but not complete answers.

I'm assuming that the final image is the problem itself.

The first question for you is: Is there any ambiguity in the direction of current flow in any of the components?

The second question is: What is the sum of the currents flowing through the two resistors and the dependent current source?

Can you write an equation for the current through the 8 ohm resistor in terms of that through the 2 ohm resistor?

Having done this, can you see how to get the answer?

 

Please answer my first question first.

 

Ok, you're wrong. Lets see why.

Firstly, how many nodes are there?

Is there any ambiguity in the direction of current flow in the independent current source?

What can you say about the direction of current flow through both of the resistors? (I.e. Can they ever be in different directions?)

Next, ignoring the dependant current source, what is direction of current flow through the 2ohm resistor?

Knowing the direction of the current flow through the 2 ohm resistor, is this the same or opposite to that through R2?

Given all of that, what can you say about the direction of current flow in the components other than the independent current source?

 

You're getting closer, but ohms should not appear.

You've got the relationship between the current through the 2ohm resistor and the dependant current source, but you need to look more carefully at the current through the 8ohm resistor.

What can you state about the voltage across both the resistors?

 

Correct

Correct

Correct

Correct

Wrong. You are saying the current flow through the 8ohm resistor is opposite to that through the 2 ohm resistor.

Haven't you already said the current flows downward in R2? are you saying it flows against the arrow in the dependant source?

Now, it could do that if the direction of current flow changed in R2 (because a -ve current multiplied by a constant is also negative) but there is no suggestion that this will happen.

Ok, your equation (whilst wrong) is kinda right, but if you don't have the signs right you will get the wrong answer.

 

Ok, so what is the current in the 8 ohm resistor in terms of the current in the 2 ohm resistor?

 

We don't give the answer.

However, once you can determine the current through the 8 ohm resistor in terms of that through the 2 ohm resistor you are able to write the equation which will give you the answer.

This should be trivial, but if you can't do it in your head, try calculating the current through a 2ohm and an 8ohm resistor with (say) 8V, 16V, and 24V across them. The pattern should be obvious.

The rest of the stuff we've been doing is to ensure you get the signs right in your equation. This is also vital or you'll make silly mistakes leading to the wrong answer.

If you need us to tell you what to do then you're not prepared to tackle this problem and you need to go back and work on simpler stuff first.

 

Highly unlikely.