circuit with 2 loops, find the current in one of the loops


by jenzao
Tags: circuit, current, loops
jenzao
jenzao is offline
#1
May24-09, 03:21 PM
P: 48
1. The problem statement, all variables and given/known data
A circuit composed of one battery and four resistors is arranged as shown in the attached pic.

E = 19 V

R1 = 12 W
R2 = 2 W
R3 = 15 W
R4 = 2 W


Calculate the current I1 through R1?




2. Relevant equations
V=IR (obviously)



3. The attempt at a solution

first i got the net current in this circuit by doing the following..
i summed resistors in series to get 14ohm on first loop and 17ohm on second loop.
then i applied resistance in parallel rule :
Req = (1/R1) + (1/R2)
= 7.69ohm = Rtotal
then I = V/R = 2.47A = total current in the circuit.

Then to get the current on the 14 ohm loopm i multiplied 2.47 by (14/17) . ( i think this is where I am erring, but cant see why this doesnt work??)

= 2.03A (wrong)
thanks for any help!
1. The problem statement, all variables and given/known data



2. Relevant equations



3. The attempt at a solution
1. The problem statement, all variables and given/known data



2. Relevant equations



3. The attempt at a solution
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jenzao
jenzao is offline
#2
May24-09, 03:39 PM
P: 48
sorry, pic pending approval --here it is uploaded to flickr...

http://www.flickr.com/photos/31088870@N02/3560817988/
earlofwessex
earlofwessex is offline
#3
May24-09, 04:20 PM
P: 87
you're making this too complicated.

the voltage between the two nodes must be the battery voltage.

so if you know the voltage accross a resistor (or an Eq Res) you can find the current through it.


use I = V/R, where R is the equivalent resistance of the branch and V is the voltage accross the branch.


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