I don't understand why the node voltage here is zero(this is for circuits class)

In summary, the teacher was going over a thevenin and norton circuit and he was trying to find Ix. He was confused when he did the node voltage at the 2 circled nodes to find Ix. He understood why the bottom node would be zero because it is the reference node but why is the top one zero? He has uploaded a picture of the notes and circled the node where he needs help with. Since it is connected to Vt wouldn't it have some voltage? Haven't you shown both nodes connected directly together? The circuit can be redrawn like this. Can you explain why the voltage at the node is zero and why the current running through the resistor is zero? Can anybody help me? Are you sure
  • #1
bambam123456
5
0
My teacher was going over a thevenin and norton circuit and i understand the thevenin and norton part of it, but the part that confused me was when he did the node voltage at the 2 circled nodes to find Ix. I understand why the bottom node would be zero because it is the reference node but why is the top one zero. I have uploaded a picture of the notes and circled the node where i need help with. Since its connected to Vt wouldn't it have some voltage?
 

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  • #2
Haven't you shown both nodes connected directly together?
 
  • #3
the circuit can be redrawn like this. Can you explain why the voltage at the node is zero and why the current running through the resistor is zero?
 

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  • #4
can anybody help me?
 
  • #5
Are you sure that bottom one is reference node?

Can you please post a full problem. I have little to work with here, and I cannot see everything clearly. Post the original schematics with variables etc.
 
  • #6
bambam123456 said:
can anybody help me?

If the "bottom node" is the reference and if you remove the apparent short circuit that you had in you first diagram then yes you are correct, the voltage at that node is not zero (unless VT=0). It is in fact [itex]4 V_T /19[/itex].
 
  • #7
how sure are you about your sketch?

i observe Vt's polarity is + up.
I observe the current source's polarity is + right so they oppose.
I can't read what is value of current source - is it 2ix ?

If so, write KVL around circuit

start at bottom of vvoltage source go ccw

-Vt + 5i5 +4ix = 0
;
;
and KCL at upper circled node

i5 -ix -2ix = 0
which yields: i5=3ix
;
;
plug into KVL equation

-Vt +5(3ix) +4ix = 0

Vt = 19ix
ix = Vt/19

what uart said

i used to make lots of mistakes from less than meticulous handwriting so i reverted to printing.

I suggest something is not transcribed correctly.
You need to work KVL and KCL until they become as natural to you as a Crescent wrench and you have confidence in them.
They will never lie, but one must be meticulous.

Believe me, i have earned the right to preach that message. "Sinners make good saints for they've learned the hard way"

what if your current source were 2i5 instead of 2ix ?

What if the question is to find value of current source that makes your node in question be zero?

check with some other students to verify you are answering right question, then show instructor what KVL and KCL have to say..be prepared, solve for the value of current source that WOULD make ix zero and show him.

old jim
 
Last edited:
  • #8
This question is well above high school level since it appears to involve a controlled current source.

We normally expect some sign of effort on the part of the student, is that evident here?
 
  • #9
Studiot said:
This question is well above high school level since it appears to involve a controlled current source.

We normally expect some sign of effort on the part of the student, is that evident here?

had the same feeling.
 
  • #10
that's a big ten-oops there, good buddies.
 

1. Why is the node voltage here zero?

The node voltage at a specific point in a circuit is determined by the difference in potential between that point and a reference point, usually ground. If the potential at both points is the same, the node voltage will be zero.

2. How do I calculate the node voltage?

The node voltage can be calculated using Kirchhoff's Current Law, which states that the sum of currents entering a node must equal the sum of currents leaving the node. This can be represented in an equation and solved for the unknown node voltage.

3. Can the node voltage ever be negative?

Yes, the node voltage can be negative. This indicates that the potential at the node is lower than the reference point.

4. What does a zero node voltage indicate?

A zero node voltage indicates that the potential at that point is equivalent to the reference point, meaning there is no voltage difference between the two points.

5. Why is it important to understand the node voltage in a circuit?

The node voltage is important because it helps us analyze and understand the behavior of a circuit. It can be used to determine the current flow and power dissipation at different points in the circuit, which is crucial in designing and troubleshooting electrical systems.

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