The sign of the current and voltage

In summary, the problem asked for the value of Iy, which was found to be 2.64 using KCL. However, the correct answer was actually negative 2.64. This is because there is a dependent voltage source with a "+ -" notation, which affects the direction of the current flow. The negative sign is significant in the final answer and must be included to accurately represent the direction of the current. Similarly, when finding V1, the correct answer was found to be -11.9 because of the chosen reference direction. It is important to pay attention to the direction of the current flow and make sure it aligns with the given figure in order to achieve the correct polarity in the answer. Additionally, it is
  • #1
525arneh
1
0
moved from general forum so homework template is missing
I was doing the following problem:

Screen_Shot_2016_02_16_at_9_16_51_PM.png


And I was asked to find Iy.

I found Iy to be 2.64 using KCL. However, the right answer was negative 2.64.

Is it negative only because there is a dependant voltage source with "+ -" ? And why must it be negative? Does "-" in the final answer play a significant role? If I put positive 2.64 instead of negative, would that be wrong?

Also, here is another question

Screen_Shot_2016_02_16_at_11_26_40_PM.png


I found V1 to be 11.9. However, the right answer was - 11.9.

Can someone clarify for me when do you put negative sign ?
 
Physics news on Phys.org
  • #2
525arneh said:
If I put positive 2.64 instead of negative, would that be wrong?

Yes, because the problem has chosen which direction the current flows for you. If the current is actually flowing in the other direction, you will get a negative value for the current because of the chosen reference direction.
 
  • #3
525arneh said:
I found Iy to be 2.64 using KCL.
You made a mistake, but by not showing your working you aren't allowing anyone to point it out.

Quite possibly you didn't solve for Iy, but instead solved for current in the direction opposite to the direction indicated for Iy. If so, that is quite okay, but you must remember before stating your answer to change its sign to correspond with the direction for Iy as specified in the given figure. Achieving the correct polarity is as essential as determining the correct magnitude; direction determines whether the designer needs to provide a power source or a power sink.
 
  • #4
+1 Show your working. Sign errors are very common when using KVL. I find it helps to write equations that sum to zero eg write them in the form..

V1 + V2 ...+ Vn = 0
 

1. What is the relationship between current and voltage?

The relationship between current and voltage is known as Ohm's Law, which states that the current through a conductor between two points is directly proportional to the voltage across the two points, and inversely proportional to the resistance between them. This means that as voltage increases, the current increases, and as resistance increases, the current decreases.

2. How do you measure current and voltage?

Current is typically measured using an ammeter, which is connected in series with the circuit. Voltage is measured using a voltmeter, which is connected in parallel with the circuit. Both ammeters and voltmeters have a high resistance, so they do not significantly affect the current or voltage being measured.

3. What is the difference between AC and DC current?

AC (alternating current) and DC (direct current) refer to the direction of the flow of electrons. In AC, the electrons alternate their direction of flow, while in DC, the electrons flow in one direction. AC is typically used for power distribution, while DC is used for electronic devices.

4. How does current affect the performance of a circuit?

The amount of current in a circuit can affect the performance of the circuit in several ways. Too much current can cause overheating and damage to components, while too little current can result in a circuit not functioning properly. The type of current (AC or DC) can also affect the performance of different types of circuits and devices.

5. What is the significance of the sign of current and voltage?

The sign of current and voltage is important in determining the direction of the flow of electrons in a circuit. In a circuit, current flows from the positive terminal of a voltage source to the negative terminal. However, in some cases, the direction of current flow may be opposite to the conventional direction due to the use of negative voltage sources or the flow of electrons in semiconductors. The sign of current and voltage is also important in calculations and determining the power and energy consumption of a circuit.

Similar threads

Engineering Determining if voltage or current is positive or negative with sources
    • Engineering and Comp Sci Homework Help
Replies
10
Views
4K
Electric Circuit Analysis, Nodal Analysis and finding Voltage.
    • Engineering and Comp Sci Homework Help
Replies
2
Views
1K
Solve Vo: Voltage Nodal Analysis w/ KCL Equation
    • Engineering and Comp Sci Homework Help
Replies
5
Views
2K
Help with Circuit Nodal Analysis
    • Engineering and Comp Sci Homework Help
Replies
2
Views
1K
Engineering Why Is Nodal Analysis Confusing in This Circuit Example?
    • Engineering and Comp Sci Homework Help
Replies
7
Views
905
Engineering Use voltage nodal analysis to solve for the current flowing in this AC circuit
    • Engineering and Comp Sci Homework Help
Replies
2
Views
1K
Engineering Why are the voltages calculated in this way? (CE BJT Amp circuit)
    • Engineering and Comp Sci Homework Help
Replies
8
Views
1K
Engineering Nodal Analysis of this Circuit using the Laplace Transform
    • Engineering and Comp Sci Homework Help
Replies
4
Views
3K
Complex RLC Circuit Problem (System of diff eqs)
    • Engineering and Comp Sci Homework Help
Replies
6
Views
769
Engineering Step response of RC circuit with independent voltage and current sources
    • Engineering and Comp Sci Homework Help
Replies
7
Views
2K

Hot Threads

Recent Insights

Back
Top