How can I come up with a equivalent resistance?

[i55BaSH]

Greetings,

I have the following circuits (picture attached):

V1 = 9 V
R1 = 1 kΩ
R2 = 7 kΩ
R3 = 7 kΩ
R4 = 0.7 kΩ
R5 = 1.5 kΩ
R6 = 1 kΩ

And I am trying to come up with an equivalent resistance so that I can calculate the voltage ( using the voltage divider formula ) at Node.

For the picture in the left I can come with an equivalent resistance:

Req_a = R3 and R4 in series as one
Req_b = Req_a and R2 in parallel as one
Req_c = Req_b and R5 in series as one

The final formula results ( under left picture ).
I have a big problem trying to come up with this approach on right picture.
Using the voltage divider formula, I just know that the equivalent resistance should be ~ 4133.6 Ω. Can you please help me?

Best regards,

 

[danadakk]

You have the V applied to the entire network, and the current going into
it. So what is the Requiv of the entire Network ? E = I x R or R = ?

Then you have a R in series with the compound network, so now what
is Requiv of a series of two R's ? Rtotal = Rseries + Requiv .........

 

[i55BaSH]

I am sorry but, I cannot follow you.

I just want to calculate the potential difference at Node ( green in pictures ) and for that I am using the voltage divider formula with R1 and a equivalent resistance.

V_Node = Req / ( Req+R1 )

In the left picture, for the red rectangle I managed to come up with a equivalent resistance for the entire block so that I can use the voltage divider formula.

In the right picture, I added the 6th resistor and I am stunned that I cannot come with the equivalent resistance for the entire orange block.

If it is not much to ask, can you help me with baby steps? Do I need to use Nodal Analysis? or is it there a method to compute a equivalent resistance for the orange block.

 

[KlausST]

Hi,

what´s the exact question?
What values are given .. and what values do you need to calculate?

Something´s wrong with circuit#2. I guess there is a problem with one given value. Please check all numbers carefully.

Klaus

 

[i55BaSH]

Hi Klaus,

At Node I want to calculate the potential difference using the voltage divider formula:

For circuit 1:

V_node = V1 * (Rb / (Ra+Rb)) -> where Ra = R1 and Rb is the equivalent resistance of R2, R3, R4, R5 as following:

(( R3 series R4 ) || R2 ) series R5

For circuit 2:

7.24V = 9V (Rb / (1kΩ+Rb))

using the voltage divider formula and knowing that on Node I have 7.24V it resulted Rb = 4133.6 Ohm as equivalent resistance.

But my question is:

How Do I arrange R2,R3,R4,R5,R6 so that it gives me that value? ( just like I explained for circuit one)

 

[barry]

you’re going to have either do a mesh analysis or node analysis. There may be another way, but that’s how i’d approach it.

 

[FvM]

To evaluate equivalent resistance incrementally, you can apply delta-wye transformation, either to R2-R4 or R4-R6. The remaining circuit can be solved by simple parallel and series resistor calculation. https://www.allaboutcircuits.com/textbook/direct-current/chpt-10/delta-y-and-y-conversions/