Kirchhoff laws

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  • #1
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1. What causes the algebraic sum of the currents (signs included) flowing into each of the four junctions NOT equal to zero?
2. What causes the algebraic sum of the EMFs in each closed loop NOT equal to the algebraic sum of all the IR drops in each loop?


For the first question, I thought that if the direction of the current flow is not maintained, like clockwise or counter clockwise, then the sum is not equal to zero
For the second question, I don't really know, I'm thinking that the circuit is not closed properly?

Thank you in advancing for helping me!
 
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  • #2
berkeman
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1. What causes the algebraic sum of the currents (signs included) flowing into each of the four junctions NOT equal to zero?
2. What causes the algebraic sum of the EMFs in each closed loop NOT equal to the algebraic sum of all the IR drops in each loop?


For the first question, I thought that if the direction of the current flow is not maintained, like clockwise or counter clockwise, then the sum is not equal to zero
For the second question, I don't really know, I'm thinking that the circuit is not closed properly?

Thank you in advancing for helping me!

Homework Statement





Homework Equations





The Attempt at a Solution


Can you please post the figure that goes with this question? There are several possible answers, but it's hard to know which one to give you hints about, without seeing the actual circuit(s).
 
  • #3
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Thank you so much! Here is the diagram
 

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  • #4
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Can you please post the figure that goes with this question? There are several possible answers, but it's hard to know which one to give you hints about, without seeing the actual circuit(s).

Thank you so much! Here is the diagram
 
  • #5
gneill
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There does not appear to be anything in the circuit in the diagram you have provided that would give Kirchoff's laws any problems.
 
  • #6
berkeman
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Thank you so much! Here is the diagram

There does not appear to be anything in the circuit in the diagram you have provided that would give Kirchoff's laws any problems.

I agree. The issues I had in mind had to do with very high frequency effects and transmission lines.
 
  • #7
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I thought so too, because we haven't learn the Kirchhoff's laws yet in class, but we have to do this for a lab. I think from the diagram, there seems to have no problems that would violate the Kirchhoff laws, but then during the performance of the actual experiment I think there may be some possible errors during the lab itself that causes problem to the laws.
 
  • #8
berkeman
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I thought so too, because we haven't learn the Kirchhoff's laws yet in class, but we have to do this for a lab. I think from the diagram, there seems to have no problems that would violate the Kirchhoff laws, but then during the performance of the actual experiment I think there may be some possible errors during the lab itself that causes problem to the laws.

Well, if there are any errors at DC in your lab, they won't be because of any problems with KCL or KVL.
 
  • #9
berkeman
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And I should say, that even at high frequencies, as long as you are careful about accounting for things, the KCL and KVL equations still apply. It would be pretty hard to work with circuits if that weren't true. You just have to be more careful about what you mean by continuity and include parasitics. No big deal.
 
  • #10
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And I should say, that even at high frequencies, as long as you are careful about accounting for things, the KCL and KVL equations still apply. It would be pretty hard to work with circuits if that weren't true. You just have to be more careful about what you mean by continuity and include parasitics. No big deal.

Thanks for the help! I did the lab today, my value for the voltage didn't add up to zero, because the errors, but it was very close to it.
 

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