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Combined Circuit problem

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


I am having trouble with the placement of the voltmeter in this particular problem


Homework Equations


What is the reading on the voltmeter V?

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The Attempt at a Solution


I found that the resistance of R is 8 ohms and the current flowing through it is 7.5 A. But I don't know how to find the voltage when the voltmeter is placed in that way :confused: I have only done voltage when the voltmeter is placed in parallel with a singular resistor only.
 
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Answers and Replies

  • #2
lewando
Homework Helper
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The voltage at the left side of the 4 ohm resistor is 100.0V, relative to Y. What is the voltage at the right side of the 4.0-ohm resistor, relative to Y? This will be the voltage appearing at the "+" terminal of your voltmeter.

The voltage at the left side of the 1 ohm resistor is also 100.0V relative to Y. What is the voltage at the right side of the 1.0 ohm resistor, relative to Y? This will be the voltage appearing at the "-" terminal of your voltmeter.

Now your voltmeter is measuring the difference of these 2 voltages (V4-ohms, right side - V1-ohms, right side)
 
  • #3
754
1
The voltage at the left side of the 4 ohm resistor is 100.0V, relative to Y. What is the voltage at the right side of the 4.0-ohm resistor, relative to Y? This will be the voltage appearing at the "+" terminal of your voltmeter.

The voltage at the left side of the 1 ohm resistor is also 100.0V relative to Y. What is the voltage at the right side of the 1.0 ohm resistor, relative to Y? This will be the voltage appearing at the "-" terminal of your voltmeter.

Now your voltmeter is measuring the difference of these 2 voltages (V4-ohms, right side - V1-ohms, right side)
Well said, except that there is no indication as to which terminal of the voltmeter is positive and which is negative. Therefore, the answer may be either positive or negative, depending on the orientation of the voltmeter (how the probes are connected).
 

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