Confused about a Result (Circuit Analysis)

  • #1
162
32
Homework Statement
Find the output voltage for the the circuit in Figure 4-22. Find the output voltage if a 500k resistor were placed across the output terminals
Relevant Equations
##\sum V = 0, \sum I = 0##
The problems I am referring to are problems 4-10 and 4-11.

There is no solution provided for 4-10, so I want to check my answer here. However, I don't understand the answer to problem 4-11. Shouldn't it also be 24 V since it is in parallel with the 200 k##\Omega## resistor? I am actually confused about resistors in parallel. Is there a chance its not in parallel due to the 50 k##\Omega## resistor on the left?
 

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Answers and Replies

  • #2
I want to check my answer here
Ambiguous :wink: ! You probably mean you want us to check your answer ? What could possibly be wrong with it ?

Re 4.11: your answer is correct. How did you calculate it ? :smile:

Hint: replace the 200 k and the 500 k resistors -- that are in parallel -- by a single equivalent resistor and repeat what you did in 4.10 !

##\ ##
 
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  • #3
Ambiguous :wink: ! You probably mean you want us to check your answer ? What could possibly be wrong with it ?

Re 4.11: your answer is correct. How did you calculate it ? :smile:

Hint: replace the 200 k and the 500 k resistors -- that are in parallel -- by a single equivalent resistor and repeat what you did in 4.10 !

Thanks for letting me know. What about 4.10, is it correct?
 
  • #4
How might the polarity of the circuit's voltage source effect your results?

It is unfortunate that the circuit diagram does not make it clear how to interpret the polarity of Vout where it is labelled.
 
  • #5
How might the polarity of the circuit's voltage source effect your results?

It is unfortunate that the circuit diagram does not make it clear how to interpret the polarity of Vout where it is labelled.
It should not. It does not matter which way the current is flowing.
 
  • #6
Ambiguous :wink: ! You probably mean you want us to check your answer ? What could possibly be wrong with it ?

Re 4.11: your answer is correct. How did you calculate it ? :smile:

Hint: replace the 200 k and the 500 k resistors -- that are in parallel -- by a single equivalent resistor and repeat what you did in 4.10 !

##\ ##
Im having trouble with 4-11. I found the equivalent resistor. I got:

##R_{eq} = \frac{200,000(500,000)}{700,000} = 143,000 \Omega##

Then I went around the circuit again with KVL. I got

##193,000 \Omega I= 30~V \implies I = 1.55 \cdot 10^{-4}~A##

But then ##V_{out} = R_{eq}I = 30V##
 
  • #7
1.55 10-4 x 143 10+3 = 30 ?

(Practising PF on a brand new phone 🤮)

##\ ##
 
  • #8
1.55 10-4 x 143 10+3 = 30 ?

(Practising PF on a brand new phone 🤮)

##\ ##
Oh no. I was using 193,000. I see now that that was wrong.
 
  • #9
Shouldn't it also be 24 V since it is in parallel with the 200 kΩ resistor?
It's in parallel so that means both resistors have the same voltage across them. It's just that the voltage is no longer 24 V.
 

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