Resistors value and current.

Hussam Mj

Joined Oct 25, 2018
17
We know that the total current is 20A and the total resistor is 5 Ohm and the voltage is 100 Volt.
How to calculate resistors and the current on R1 , R2, R3

Thanks

Last edited by a moderator:

ericgibbs

Joined Jan 29, 2010
11,651
hi Hussam,
Welcome to AAC.
E

Hussam Mj

Joined Oct 25, 2018
17
resistor (R1) emits an effect twice the size
like the other (R2). The third (R3) emits a power of 1.2 kW.

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MrChips

Joined Oct 2, 2009
22,569
Have you studied the question?
Is the solution a unique one, i.e. there is only one solution for R1, R2, and R3?

WBahn

Joined Mar 31, 2012
26,398
We know that the total current is 20A and the total resistor is 5 Ohm and the voltage is 100 Volt.
How to calculate resistors and the current on R1 , R2, R3

Thanks
Based on just what you have given, let's look at a couple possible scenarios.

To make things simple, let's stipulate that R1 and R2 are equal.

Now let's say that R3 = 1 Ω. What are R1 and R2?

Now let's say that R3 = 4 Ω. What are R1 and R2?

Do you see the problem?

WBahn

Joined Mar 31, 2012
26,398
resistor (R1) emits an effect twice the size
like the other (R2). The third (R3) emits a power of 1.2 kW.
Now you seem to be throwing out additional information that wasn't in the first post? You can't expect much meaningful help if you don't include all the information.

What "effect" is "emitted" by a resistor? Voltage? Current? Power?

Are you saying that R1 dissipates twice the power of R2 and that R3 dissipates 1.2 kW?

Hussam Mj

Joined Oct 25, 2018
17
That was the first part of the question.
I mean, Power .
R3 dissipate 1.2 KW . R1 dissipate double R2.

WBahn

Joined Mar 31, 2012
26,398
In your work, you somehow conclude that the parallel resistance of R1 and R2 is 2/3 (presumably 2/3 Ω since you have to add this to R3 to get Rtot).

What is your basis for this conclusion?

If you know that the total current is 20 A and that the power dissipated in R3 is 1.2 kW, what can you conclude about R3?

Hussam Mj

Joined Oct 25, 2018
17
R3 = 8,3 Ohm

No basis on what I gave R1 the value 1 ohm, but only to get close to find the values of the other resistors.

WBahn

Joined Mar 31, 2012
26,398
R3 = 8,3 Ohm
That's not correct, but I can't tell you where you made your mistake unless you show your work.

No basis on what I gave R1 the value 1 ohm, but only to get close to find the values of the other resistors.
Engineering is not about guessing. By guessing a value and then basic the rest of your work off that, you pretty much guarantee that all of your results will be wrong.

bertus

Joined Apr 5, 2008
21,056
Hello,

I have enlarged the image a bit for better readability:

You know that the power dissipated in R3 is 1.2 kWatt.
You also know that total current is 20 Amp.
What would be the resistance of R3?

Bertus

Hussam Mj

Joined Oct 25, 2018
17
The calculation is based on Ohm law, but the total resistance is 5 Ohm

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bertus

Joined Apr 5, 2008
21,056
Hello,

The given 1.2 kWatt is for R3 only and not for the complete circuit.

Bertus

Hussam Mj

Joined Oct 25, 2018
17
I was mistaken, I did the calculation for the complete circuit.
The total should be 2000 Watt, and since R3 dissipate 1200 watt so R1 and R2 dissipate 800 watt!

bertus

Joined Apr 5, 2008
21,056
Hello,

You will probably know the Ohms laws Wheel:

Now use the given power and current for R3 to calculate the value of R3.

Bertus

Hussam Mj

Joined Oct 25, 2018
17
Thank you for pointing out.

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bertus

Joined Apr 5, 2008
21,056
Hello,

Correct, the value of R3 is 3 Ohms.
The value of R1 and R2 in parallel is 5 - 3 = 2 Ohms.
What is the relation between R1 and R2?

Bertus

Hussam Mj

Joined Oct 25, 2018
17
What about that R1 dissipate double power R2.

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bertus

Joined Apr 5, 2008
21,056
Hello,
The total should be 2000 Watt, and since R3 dissipate 1200 watt so R1 and R2 dissipate 800 watt!
Knowing that R1 and R2 are dissipating 800 watts total, you can calculate the power of each resistor.

Bertus

WBahn

Joined Mar 31, 2012
26,398
The calculation is based on Ohm law, but the total resistance is 5 Ohm
The problem is that you don't understand Ohm's Law or the power equation.

Ohm's Law related the resistance of a resistor to the current through THAT resistor and the voltage across THAT resistor.

Similarly, P = V²/R relates the power dissipated by a resistor to the voltage across THAT resistor and the resistance of THAT resistor.

What you are doing is blindly throwing the nearest voltage value at the nearest V in a formula without any regard whether or not that voltage is actually the voltage across THAT resistor.