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Ratchit said:
ericgibbs,



Thanks Eric, I needed that. Now if you would be so kind as to present a confirmation of the problem answer using constant voltage sources, then I can go to bed.

Ratch
Click to expand...

hi Ratch,

I could consider using constant voltage sources in the problem network, but we both know that the source symbols are standard Constant Current sources, not Constant Voltage sources.

Go to bed and rest easy

Eric


EDIT:
Added a link to help out the non believers.

https://www.rapidtables.com/electric/electrical_symbols.htm
 
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Taking just the 36v 3R and 18R we get:
The current through the 18R is 36/21 = 1.71A
The voltage across the 18R is 18 x 1.71 = 30.78v
The wattage is 52.63watts

Replacing the 18v and 6R is simply going to load the circuit and reduce the voltage across the 18R, so the dissipation is nothing like the 108watts maximum.

[MODNOTE]Removed unnecessary comments.[/MODNOTE]
 
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What you dont seem able to grasp, is that the sources are Constant current and NOT constant voltage.!!

I cannot imagine what you have been 'teaching' for the past 30 years, but it certainly was not electronics.

Any first year student in a Univ degree course would have been taught to recognise the difference between a constant current and constant voltage source symbol.

If you want me to describe the definition of a constant current source, let me know and I will explain for you.

Is it possible you could post some information regarding any professional qualifications that you may have to support your claim that Ratch and my answers are 'silly', as its important the OP gets the correct guidance on this problem. ?
 
Interestingly you have edited the OP's original diagram on your web site in order to correct your mistake.

Where have the Polarity and Voltage symbols come from ? and whats happened to the current direction arrow.??
 
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We need to go back to the original provider of the circuit to find out if the circuit is intended to be a simple voltage analysis or current analysis.
I took it as a voltage circuit from a beginner.
 
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colin55 said:
First of all, this is a DC circuit. So what bearing does a constant voltage or constant current source have on the outcome?
Click to expand...

This statement tells me all I need to know in reply to my question regarding your electronics qualifications.

I see that once again you have edited your earlier post.

EDIT:

We need to go back to the original provider of the circuit to find out if the circuit is intended to be a simple voltage analysis or current analysis.
I took it as a voltage circuit from a beginner.
Click to expand...

If you have mistaken the circuit in assuming they are voltage sources, I could accept that as reason for your confusion.
 
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The diagram is not clear enough as to the value of 36 and 18. If it is current, it turns a simple diagram into a very complex calculation.
For constant current, the arrow should be within the symbol.
As I said, the source of the circuit should be determined to find out the intended complexity.
Simple things such as labels "A" "V" and "R" whould save a lot of frustration.
 
Colin55,

The diagram is not clear enough as to the value of 36 and 18. If it is current, it turns a simple diagram into a very complex calculation.
Click to expand...

Not at all. Calculating for constant current sources is no problem. In any case, I did a node analysis for both cases, so everything is covered. Your calculation assuming voltage sources is just plain wrong.

Ratch
 
I would like to go back to the original supplier of the circuit because the values have been selected so that once you realise the value of Rx is 3R, the circuit is easy to analyse.
 
colin55,

I have already shown that the wattage dissipated in 2R is less than 103 watts. .
Click to expand...

Your calculations were wrong for the reasons already given. Don't you believe or understand the computer simulation Eric was kind enough to run? And how it agrees with my node calcuation? Can you explain the mistakes in his or my presentations?

Ratch
 
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The graph uses voltage sources for 36 and 18.
Do a simple Ohm's law assessment.
I don't consider the problem was intended to be such a complex issue.
 
colin55,

The graph uses voltage sources for 36 and 18.
Click to expand...

Certainly, isn't that what you used for your calculations?

Do a simple Ohm's law assessment.
Click to expand...

A node analysis does a voltage/current/resistance assessment. So does a computer simulation.

I don't consider the problem was intended to be such a complex issue.
Click to expand...

Complexity is not the issue, correctness is. Where is the complexity?

Ratch
 
The problem is a simple Ohm's Law example, when you realise the maximum dissipation occurs when Rx is 3R.
 
colin55,

The problem is a simple Ohm's Law example, when you realise the maximum dissipation occurs when Rx is 3R. .
Click to expand...

Yes, the problem is fairly simple. You have not proven what you contend is the correct answer. Both Eric and I have done so for our answers, and you have not proved us wrong. Now it is your turn. Just saying so is not proof. Show us the calculations, but not the wrong ones you presented before.

Ratch
 
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