Register to reply

Can someone help me with 2 circuit problems...please

by supermenscher
Tags: circuit, problemsplease
Share this thread:
supermenscher
#1
Jun28-04, 12:47 PM
P: 47
1. The equivalent resistance between points A and B of the resistors shown below is 38 ohms. Find the value of the resistance R.

The resistor looks like this
55 Ohms

_____\/\/\/\/_____
| |
12 Ohms | |
A | |
.____/\/\/\__ | |______. B
| |
| |
|____\/\/\/\/_____|
R

I have no idea what to do...please help.


2. Determine the magnitudes and directions of the currents through R1 and R2, where R1 = 36 ohms and R2 = 10 ohms. I already found the directions. they are both from right to the left, I just need the magnitudes. The Bs represent batteries, and the + next to them indicates the positive side of the battery. I am also really lost on this one can anyone help?

V1=9.0V R1
--+B--/\/\/\-------
| |
| R2 |
.-----/\/\/\/-------.
| |
| |
|----------B+------|
V2=6.0V
Phys.Org News Partner Science news on Phys.org
What lit up the universe?
Sheepdogs use just two simple rules to round up large herds of sheep
Animals first flex their muscles
AKG
#2
Jun28-04, 03:27 PM
Sci Advisor
HW Helper
P: 2,586
I would suggest using [ code ] and [ / code ] tags:
                             55 Ohms
                       
                      _____\/\/\/\/_____
                      |                 |
       12 Ohms        |                 |
   A                  |                 |
   .____/\/\/\_______ |                 |______. B
                      |                 |
                      |                 |
                      |____\/\/\/\/_____|
                               R

                            
                            V1=9.0V     R1
                               --+B--/\/\/\-------
                               |                  |
                               |         R2       |
                               .-----/\/\/\/-------.
                               |                  |
                               |                  |
                               |----------B+------|
                                          V2=6.0V
EDIT: Well, it looks best in the editor window, slightly better (but not great) in the code tags, and unreadable without those tags.

SECOND EDIT: looks fine now

------------------------------------------------------------

For the first question, you should know how to calculate net resistances when you have resistors in series and parallel. To find the total resistance between A and B, it is:

[tex]R_{total} = 12 \Omega + (55 \Omega || R)[/tex]

[tex]38 \Omega = 12 \Omega + (\frac{1}{55 \Omega} + \frac{1}{R})^{-1}[/tex]

[tex]26 \Omega = (\frac{1}{55 \Omega} + \frac{1}{R})^{-1}[/tex]

[tex](\frac{1}{26 \Omega} - \frac{1}{55 \Omega})^{-1} = R[/tex]

[tex]R \approx 49.310 \Omega[/tex]

[tex]R = 49 \Omega[/tex]

-----------------------------------------------------------

Solve question 2 using the principle of superposition. That is, find the voltages and currents with the circuit first by replacing the top battery with a short circuit, then find the voltages and currents with the top battery, replacing the bottom with a short circuit. Add the numbers from the first calculations to the second calculations, and make sure you take direction/sign into account.
supermenscher
#3
Jun28-04, 06:34 PM
P: 47
Thank you so much, I got them both right and 100 on the assignment :) :) :)


Register to reply

Related Discussions
Basic Circuit Problems - KVL and KCL Engineering, Comp Sci, & Technology Homework 6
More circuit problems Introductory Physics Homework 4
Circuit problems Electrical Engineering 8
A couple circuit problems.. Introductory Physics Homework 8
DC circuit problems Introductory Physics Homework 13