Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

simple circuit problem using KVL and KCL

Status
Not open for further replies.

PG1995

Active Member
Hi:)

Please have a see on this circuit diagram:
https://img192.imageshack.us/img192/7726/meshkvl.jpg

Note: "1", "2", "3" coming after the "I" are subscripts.

I used these equations:
1: I1 = I2 + I3 (Using KCL at junction e)
2: 6 - 4I2 + 4 - 2I2 = 0 (Using KVL around afeba)
3: 3 - 6I3 - 4 - 4I2 = 0 (Using KVL around dcbed)

I2 = 2.8 A

I1 = 4.5 A

I3 = 1.7 A

I don't understand where I'm wrong. Perhaps the error lies somewhere in the approach. Would you please help me with it? Thanks.
 
First, lets see what LTSpice says: (note I swapped the position of V2 and R2 to make it easier to visualize. I also labeled the nodes differently than you).

Now, using algebra:
Code:
Σ of currents into node B = 0 

I1 + I2 + I3 = 0

I = V/R


[V(c)-V(b)] + [V(d) -V(b)] + [V(e)-(V(b)]
--------      -----------    -----------          =   0
    2             4              6


6[-6-V(b)] +  3[4-V(b)]  +  2[3-V(b)]
-----------------------------------            = 0
               12

-36 -6V(b) +12 -3V(b) +6 -2V(b) = 0 


-3V(b) -6V(b) -2V(b) = 36 -6 -12

-11V(b) = 18

V(b) = -18/11 = -1.36363


Now that you know V(b), you can solve for the branch currents.
 

Attachments

  • DF181.png
    DF181.png
    18.6 KB · Views: 229
Last edited:
MikeMl,

I believe you reversed the battery V3. The voltage at node b should be -18/11 = -1.64 .

PG1995,

The node equation is (Vb+6)/2 + (Vb-4)/4 + (Vb-3)/6= 0 ======> Vb=-18/11 = -1.64

Ratch
 
MikeMl, Ratchit, BrownOut, I'm very thankful to all of you. MikeMl, I do have some questions on LTspice which I will ask soon. I have it installed it on my computer but don't know how to use it. I also have Qucs program.

Once again, thank you.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top