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Home Q & A Board Science-Related Homework Help Physics
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ritamonteiro ritamonteiro
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11 years ago
Guys i need your help on this one....

In the circut below R1 and R2 are in parallel and R3 is in series with this combination. There is no immediate place to calculate a voltage drop by Ohm's Law because none of the resistors has both a known current and resistance. Neither can the total resistance be obtained because R2 is unknown. So how can i find the current in R3 by applying Kirchhoff's current Law to node A?

Here is the circuit:
http://img106.imageshack.us/img106/2241/circuitfw5.png

Guys please explaining it simply for me. In the simplest way you worked out the current for R3
The current has the positive side to R2 and the negative end towards the node (R3) area
Java of course thats 100% possible.
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3 Replies
Replies
wrote...
#1
11 years ago
is the 1mA a current generator or given current? and what direction is it going?

Assuming the current is given as 1mA to the left and not a current generator producing a 1mA current to the left.
 You could use Kirchoff's voltage law by setting up two loop equations and setting up a third equation for the known 1mA current.
Wher I1 is the "current" going clockwise in the top loop and I2 is the current clockwise in the bottom loop.
The equations would look like this
0.001 = I1 - I2
0 = I1 (56000) + I1 (R2) - I2 (R2)
76 = - I1 (R2) + I2 (56000) + I2 (R2)
now you have 3 equations with 3 unknowns and you can solve for all of them
The cuurent going through R3 will be equal to the current value of I2
wrote...
#2
11 years ago
R1 and R2 are parallel and in series with R3

but since there is no resistance given in the parallel circuit u cannot calculate the total current in R3

But the current thru R1 + R2 = R3

unless im stupid
thats possible!
Answer accepted by topic starter
mickey16mickey16
wrote...
#3
Posts: 40
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11 years ago
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