Question

here's another exercise in analyzing circuits. help me please! :D

Answer 1

how to assign the currents?

Answer 2

this is the special case ,have u learned about supernode??

Answer 3

no, i don't have much learning about this stuff. sorry! please teach me.

Answer 4

What is the value on the voltage source on the right? It looks like +V.

Answer 5

4 maybe?

Answer 6

it is 4v. the voltage source on the right.

Answer 7

sure :)
u see the node above 18 ohm register ,lets call it V1
u see the node above 3 ohm register ,lets call it V2
now since V1 is directly attached to negative terminal of the 20V battery and
V2 is directly attached to positive terminal of the 20V ,
we can write one equation as V2-V1=20
ok till here?

Answer 8

ok. i get it. :)

Answer 9

then?

Answer 10

now as u know some basics of nodal,what i write will make sense to u
for V1--->V1/18 +(V1-2)/3
for V2---?V2/3+(V2+4)/8
making sense?

Answer 11

V1 - 2? or is it v1 - v2? sorry, i'm quite confused.

Answer 12

its (V1-2)/3

Answer 13

why should V2 come into that picture??

Answer 14

no, i just thought u misread the values in the drawing. is 2 the voltage source in the right?

Answer 15

to the left...to the right u said it to be 4 V

Answer 16

or its 42V??

Answer 17

yes, sorry. the left voltage source is 42v. sorry!

Answer 18

i think its 42 V!!

Answer 19

then it will be (V1-42)/3....isn't it?

Answer 20

yes! yes! but why not 42-v1?

Answer 21

Here is what I've drawn... I will change that to 42, but check the v1 and v2 I drew.

Answer 22

The 4's looked like plus signs, I think we are all on the same page now.

Answer 23

ohh! that i forgot to mention that I will assume all the currents leaving the node
so (V1-42) and not (42-V1)

Answer 24

ok. but is it alright if i assume the current to enter the nodes?

Answer 25

yes,you can assume,in that case u should take (42-V1)

Answer 26

That will stretch my brain. ;)

Answer 27

ok,so we all understood till here,right?
what @EulerGroupie drawn is correct(except 42 instead of 2)
now going ahead,we need 2nd equation in V1 and V2 to get both these values(as we have one equation already....difference 20)

Answer 28

I think that I'm with ya'. How about you @lilMissMindset ?

Answer 29

i am as well! i am trying my best here to cope! :D

Answer 30

now i will add all those 4 currents and equate it to 0 for my 2nd equation:
V1/18 +(V1-2)/3+V2/3+(V2+4)/8 = 0
now u have 2 equation,2 unknowns
can u solve for V1 and V2??

Answer 31

ummm. why equate it to 0? what i'm thinking is that i am going to equate it to 20. lol me

Answer 32

no,20 i have already considered in 1st equation,here the method says to equate it to 0

Answer 33

ok then i'll do it.

Answer 34

V1/18+(42-V1)/3+V2/3+(4+V2)/8=0 with currents flowing out and changing 2 to 42?
That's why its Supernode, huh? Like smashing 2 nodes into one... but with a catch.

Answer 35

yes,u got it right @EulerGroupie thats y its supernode...
now u both tell V1 and V2

Answer 36

Now how do you calculate the power that is provided only by the 20 Volt source? Wasn't that the problem?

Answer 37

You always keep the question in mind don't ya'? Right on!

Answer 38

i am asking for V1 and V2 for the 4 currents,which i will use to find power..

Answer 39

I am puzzled by this circuit, it looks like the source on the right is not providing power at all, maybe even absorbing power ??

Answer 40

It can happen.

Answer 41

I'll step in front of this bus... I got V1=-18.878V and V2=1.122V. Agree/disagree?

Answer 42

I agree that the difference does indeed equal the required 20 volts.

Answer 43

i got v2=25.115v and v1=5.115v

Answer 44

OMG! i haven't solved it myself,thinking u both will get the same answer...now i have to :(

Answer 45

And the difference does equal the required 20 volts for lilMissMindset

Answer 46

Yeah, intuitively mine seems off. I'll check.

Answer 47

We will get there.... ty @hartnn

Answer 48

The two answers, although different, do have a difference that is close to the 20 volts that is the difference of V1 and V2. Maybe signs??

Answer 49

u both sure u both took 42V instead of 2 V ??

Answer 50

i used 42v

Answer 51

For total power I got 72 watts, but don't have a clue how much of that is from the 20 volt source of if it is even the correct total power.

Answer 52

I went back to my comfort zone of current outward and got v1=4.71 and v2=24.71.

Answer 53

Yeah getting there.

Answer 54

how did u get the power @radar?

Answer 55

I thevenized each side left and right put the 20 volt source between them. However, I am not at all comfortable with that method.

Answer 56

what current did you find for 20v source?

Answer 57

I have found 12.0109A

Answer 58

@lilMissMindset ,left source is 42V ?

Answer 59

yes, 42 v. right is 4v

Answer 60

That is a lot more than my 2.8 amps, no wonder I am not comfortable.

Answer 61

@EulerGroupie did u get correct V1 and V2?

Answer 62

this question would have been much simpler with ckt reduction technique...but we have to use nodal as said.....

Answer 63

maybe the discrepancy is due to rounding off values.

Answer 64

Agreed.

Answer 65

i am getting exact 5.11 as V1,thats y waiting 4 u...@EulerGroupie

Answer 66

Waiting with abated breath for the power provided by the 20 volt source!

Answer 67

if the resistances are : 3,18,3,8 from left to right
i'm sure from my answer of current of 20v source

Answer 68

I have an arithmetic error somewhere. My left current should equal my right current... right now I'm between 10.82 and 12.169 amps. Still checking.... I bet you're right.

Answer 69

2.885M Watts

Answer 70

Hey that agrees with @lilMissMindset.

Answer 71

wich one @radar ?

Answer 72

The 5.11 for V1

Answer 73

wich node do you take as V1?

Answer 74

V1 was the label for the node above the 18 Ohm resistor.

Answer 75

Yeah, that gets 12.013A going through the 20V source from the left. Power from that is 12.013 time 20 equal to 240.26 W

Answer 76

it would be better you take it as one single supernode

Answer 77

ok,here is what i propose:
since now u know V1 and V2,u can find all the currents
hence u can find power absorbed/delivered by all resistors and voltage sources except 20V right??
now since total(sum of all)powers in a circuit=0,we can get power by 20v source
@lilMissMindset @EulerGroupie

Answer 78

right

Answer 79

240.21W

Answer 80

do u have options or answer? @EulerGroupie @lilMissMindset

Answer 81

Yes! 5.11V and 25.11V balances the circuit. I got 12.013A on the left and 12.001A on the right. Rounding errors obviously. I would probably just say 240W and call it good.

Answer 82

This was all for @lilMissMindset . Are you satisfied with this?

Answer 83

Thanks everyone as my curiosity was way up there.

Answer 84

I used mesh current analysis (which I am very comfortable with) and let my calculator do the matrices and got exactly 12.0109A through the 20V source. Multiplying gives 240.218 Watts.
If the question had been : do it how you want. Mesh with a calculator took a few minutes.

Answer 85

yes. i think i'm getting it, sorry i am quite a slow learner. thanks everyone for the help! i hope you enjoyed helping me
.

Answer 86

Loved it! Thank you. :D

Answer 87

always happy to help :)

Answer 88

Make sure you medal @hartnn on your way out.

Answer 89

sure. thanks a lot again. if i can give all of you medals, i will. thanks again. :)