Negative conundrum

[Kevineamon]

 

Guys can anyone see where I'm getting these negative values from. Probably need to sleep tbh. I know it's probably that -36 but I can't think why, it shouldn't be so...

 

Any ideas would be great.

[Bender]

Why is iy=-36 A?

[studiot]

I don't understand your labeling in the diagram.

 

You have written 2i_x in blue against the controlled current source, which suggests it is defined in the problem.

 

But you have written i_x in red as though it was your naming of the branch currents at the nodes.

 

Please explain.

[Kevineamon]

You are correct about the blue - Those are predefined. The Ix, the little Ix on the wire, is also defined in the problem. I just always label currents in red.

The rest of the currents are my own naming convention.

 

As for the -36 Bender. It looks to me as if 36 is travelling into V2. Therefore IY should be negative.... I think....

[studiot]

There is still something missing.

 

You say 2i_x is defined in the problem as I suspected, but you haven't told us what it is.

I did ask for more explanation.

 

A tip about the node Law. At least one of the currents at any node must be of opposite direction to the others, unless they are all zero.

The sign that comes out of solving the equations tells you whether you have guessed the direction correctly or not.

[Kevineamon]

Ok so then

 

ix = -48 / 4 = - 12 A

across the 4 ohm resistor....

 

Ahh ok I think I see...

[Bender]

As for the -36 Bender. It looks to me as if 36 is travelling into V2. Therefore IY should be negative.... I think....

But where did you get the value from? Was it given? It appears that you have three unknowns, but you used only two equations.

[studiot]

This whole question is rather puzzling.

 

It is puzzling because the material is not taught until a specialised course in electronic engineering at University or College.

It is not even always taught in similar level electrical engineering course.

 

Previously you struggled with some much simpler problems that might have been offered in Physics at A level in secondary education.

 

You have said that you are preparing for imminent exams, so what are you studying?

 

We want to help but it would be really useful to know where you are coming from.

 

Back to the question.

 

You have a circuit with 5 elements, three of which do not obey Ohm's law and two of which do.

 

In the circles you have a fixed current source of 12A and a fixed voltage source of 36V.

 

You seem to have added 12 amps to 36 volts at some stage in your figuring?

 

In the diamond you have a current controlled current source of value 2x_i where x_i is a circuit variable from somewhere else in the circuit.

 

Unfortunately you have not told us what the question says about x_i

 

There are 6 loops in the arrangement, but not all of them represent independent equations.

 

I have said to you before you should redraw a circuit into the most convenient form (teachers like to obfuscate to exercise the mind)

and that you should get used to recognising small series and parallel arrangements.

 

I have done this below, the second diagram shows your circuit in standard form.

 

Note the current sources are working in opposing directions.

 

Edited April 6, 2017 by studiot

[Kevineamon]

Hi Studiot - I'm an undergraduate studying electrical and electronic engineering. Perhaps my questions might be better placed in an electronics forum? They're becoming quite complex. I'm slightly older than the other students. Unfortunately some of the younger folks, in their wisdom, decided to complain about the lecturing staff. My Easter work load seems to reflect the outcome of said complaint...

 

They say - "youth is wasted on the young." They were right imho... sigh...

Edited April 9, 2017 by Kevineamon

[studiot]

We have had several students reports heavy Easter workloads

It's all a dastardly plot by the establishment to keep them from enjoying that wonderful weather we are currently having.

 

 

Rest assured there are plenty of competent responders here for your field.

It's good to try to develop a relationship as folks are more willing to help when they know you a bit.

 

A tip

 

Wherever you go for help and advice (the web, college, books...) always establish the engineering conventions in use at the outset.

There are a number of contradictory conventions so find out quickly to avoid cross purposes.

 

There used to be a non profit teaching site and forum called

 

allaboutcircuits.com

 

They were very friendly and I had many good conversations there.

 

But they have been taken over by commercial interests so there is always a hidden agenda there these days advertising certain products.

About half of the excellent specialists left when the takeover happened, and I don't visit often

now myself.

Edited April 10, 2017 by studiot