Finding Terminal Voltage

  • Thread starter rizardon
  • Start date
  • #1
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Homework Statement


In the circuit shown in the figure below the current through the 12.0V battery is measured to be 70.6 mA in the direction shown. What is the terminal voltage Vab



Homework Equations


V=E-IR
I1=I2+I3


The Attempt at a Solution


First I set Vab= E-IR= 24 - 10(I1)
I1=I2 + I3
So I applied Kirchoff's rule on the outer loop to find I3
-12 - 10I2 + 20I3 = 0
I3= [12 + 10I2]/20 = 0.6000353 = 0.6A
I1= I2 + I3 = 70.6 mA + 0.6A = 0.6000706A = 0.6A
Vab= 24 -10I1 = 24 - 6 = 18V
Is this right?
 

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Answers and Replies

  • #2
vela
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What happened to the 30-ohm resistor?

The voltage due to the internal resistance of the 12-volt battery is (70.6 mA)(10 ohms) = 706 mV = 0.706 V. You seem to have divided by another factor of 1000.
 
  • #3
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Can I combine the 20(ohm) with the 10(ohm) resistor?
 
  • #4
vela
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No, because they're neither in series nor in parallel. You could, however, combine the 20-ohm and 30-ohm resistors because they're in parallel.
 

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