Find the current

  • Thread starter Gauss M.D.
  • Start date
  • #1
153
1

Homework Statement



Find the current marked I3 in the circuit.

Homework Equations





The Attempt at a Solution



The voltage over R2 and R1 is the same. The current I0 (12mA) is the sum of I2 and I1.

I1*R1 = I2*R2:
4*I1 = 1.25*I2

I1 + I2 = 12 <=> I2 = 12 - I1

4*I1 = 1.25*(12 - I1) = 15 - 1.25I1
5.25*I1 = 15

I1 = 2.86

I think I've messed up already here. Can anyone spot what I'm doing wrong??
 

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  • #2
ehild
Homework Helper
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1,909

Homework Statement



Find the current marked I3 in the circuit.

Homework Equations





The Attempt at a Solution



The voltage over R2 and R1 is the same. The current I0 (12mA) is the sum of I2 and I1.

I1*R1 = I2*R2:
4*I1 = 1.25*I2
It is wrong. The voltage over R3 and R4 is the same .

I1 + I2 = 12 <=> I2 = 12 - I1

4*I1 = 1.25*(12 - I1) = 15 - 1.25I1
5.25*I1 = 15

I1 = 2.86

I think I've messed up already here. Can anyone spot what I'm doing wrong??
 
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  • #3
153
1
Thanks! Is I2 still the sum of I3+I4 though? :S
 
  • #4
gneill
Mentor
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