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Given what else you know about the power dissipated by R1 and R2, can you now determine how much power is dissipated by R1 and how much is dissipated by R2?
Resistors value and current.
- Thread starter Hussam Mj
- Start date
Given what else you know about the power dissipated by R1 and R2, can you now determine how much power is dissipated by R1 and how much is dissipated by R2?
Well, let's see if it meets the requirements.
Does R1 dissipate twice the power as R2?
Pr1 =?= 2·Pr2
533 W =?= 266 W
Yes (within roundoff -- and you should round 266.6666... W to 267 W).
Does R3 dissipate 1.2 kW?
Pr3 = (20 A)² · (3 Ω) = 1200 W
Yes.
Does the total power equal the total voltage applied to the total equivalent resistance?
Ptot = Vtot² / Rtot = (100 V)² / (5 Ω) = 2000 W
Ptot = Pr1 + Pr2 + Pr3 = 533 W + 267 W + 1200 W = 2000 W
Yes.
Look good so far.
Do you see how I did these checks? You need to start learning how to check your own work -- there won't always be someone around to do it for you.
Now, can you see a way to find the voltage across R1 and R2?
I think you are making progress, but you have a bookkeeping train wreck in your work.
Look at just your last two lines. You first claim that Rtot = 2Ω and then that Rtot = 5Ω. Which is it?
Don't use the same symbol for more than one thing -- it causes nothing but confusion and is a recipe for disaster.
This problem has the following symbols defined: R1, R2, and R3. Those symbols refer to specific resistors in the circuit you are working with. Anytime you have an R3 in your work for this problem, it should refer to the resistor that is in series with the power supply and anytime you use R1 it should refer to the rightmost resistor. You also quickly use the notion of the total circuit resistance needing to be 5 Ω through
Rtot = 100 V / 20 A = 5 Ω
That now establishes Rtot as being the total circuit resistance as seen by the supply. Don't use Rtot for anything else from that point on.
So when you want to use a generic equation, such as
Rtot = (R1·R2) / (R1 + R2)
Translate it into the symbols in the circuit. If you want the parallel resistance of R1 and R2, you might use
R12 = (R1·R2) / (R1 + R2)
When you want to use the generic series resistance formula
Rtot = R1 + R2
You need to similarly translate it, so here you would have
Rtot = R3 + R12
The other big thing you need to start doing is properly tracking your units. I just made a post in another thread on this very point that you might find useful.
https://forum.allaboutcircuits.com/threads/electrical-and-electronic-question.153425/#post-1318053
Look at just your last two lines. You first claim that Rtot = 2Ω and then that Rtot = 5Ω. Which is it?
Don't use the same symbol for more than one thing -- it causes nothing but confusion and is a recipe for disaster.
This problem has the following symbols defined: R1, R2, and R3. Those symbols refer to specific resistors in the circuit you are working with. Anytime you have an R3 in your work for this problem, it should refer to the resistor that is in series with the power supply and anytime you use R1 it should refer to the rightmost resistor. You also quickly use the notion of the total circuit resistance needing to be 5 Ω through
Rtot = 100 V / 20 A = 5 Ω
That now establishes Rtot as being the total circuit resistance as seen by the supply. Don't use Rtot for anything else from that point on.
So when you want to use a generic equation, such as
Rtot = (R1·R2) / (R1 + R2)
Translate it into the symbols in the circuit. If you want the parallel resistance of R1 and R2, you might use
R12 = (R1·R2) / (R1 + R2)
When you want to use the generic series resistance formula
Rtot = R1 + R2
You need to similarly translate it, so here you would have
Rtot = R3 + R12
The other big thing you need to start doing is properly tracking your units. I just made a post in another thread on this very point that you might find useful.
https://forum.allaboutcircuits.com/threads/electrical-and-electronic-question.153425/#post-1318053
