Using Kirchhoff's law, deduce the value and direction of the current

In summary, according to Kirchhoff's law, the value and direction of current I can be deduced as -2A entering from the top of the diagram. This may seem counterintuitive, but it is due to the nature of Kirchhoff's law and the fact that the positive or negative designation of current is based on the direction of the arrow on the diagram, not the actual direction of the current itself. Therefore, in this case, the current is actually entering the wire from the top, even though the arrow is pointing in the opposite direction. This satisfies Kirchhoff's law, as the current entering and exiting the wire is balanced.
  • #1
haha0p1
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9
Homework Statement
Use Kirchhoff's law to deduce the value and direction of the current I.
Relevant Equations
Current entering a point is equal to current exiting a point
3 A+ 2 A = 7 A+ I
I = -2A
How the current can be in negative direction? If the sign if negative, doesn't it mean that the current will move towards the point P? Also If I am taking the 2A to be positive then Kirchhoff's law isn't satisfied as 5A≠7A
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  • #2
haha0p1 said:
Homework Statement:: Use Kirchhoff's law to deduce the value and direction of the current I.
Relevant Equations:: Current entering a point is equal to current exiting a point

3 A+ 2 A = 7 A+ I
I = -2A
How the current can be in negative direction? If the sign if negative, doesn't it mean that the current will move towards the point P?
The arrow on the diagram indicates the positive direction for current ##I##. It's doesn't imply the current itself is in the positive direction.
 
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  • #3
PeroK said:
The arrow on the diagram indicates the positive direction for current ##I##. It's doesn't imply the current itself is in the positive direction
Even If I take the value of I to be 2 A, Still my current entering the wire and current exiting the wire is not the same as 3+5=7+2
And 5≠9
 
  • #4
haha0p1 said:
Even If I take the value of I to be 2 A
Why would you do that?
 
  • #5
PeroK said:
Why would you do that?
Because The question is asking to find value of I which is coming 2
 
  • #6
haha0p1 said:
Because The question is asking to find value of I which is coming 2
##I \ne 2## as you yourself have already established. And, you seem to know that ##I = -2## but have decided that current must be positive. That puts you in an impossible position in this case.
 
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  • #7
think of it this way:

If you designate a current leaving a node as positive and it mathematically turns out negative via KCL then that current is actually entering.

What’s really happening is that

3A is entering from the right
2A is entering from the bottom
2A is entering from the left

7A is leaving from the top
 
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1. What is Kirchhoff's law?

Kirchhoff's law, also known as Kirchhoff's circuit laws, are two fundamental principles in circuit analysis that govern the behavior of electric currents. They are named after German physicist Gustav Kirchhoff and are widely used in the study and design of electrical circuits.

2. How do Kirchhoff's laws relate to current?

Kirchhoff's laws state that the total current entering a junction in a circuit must equal the total current leaving the junction, and that the sum of the voltage drops in a closed loop must equal the sum of the voltage sources in that loop. These laws are essential in determining the value and direction of the current in a circuit.

3. How do I use Kirchhoff's laws to deduce the value of the current?

To use Kirchhoff's laws to deduce the value of the current, you must first draw a circuit diagram and label all the components and the direction of the current. Then, apply Kirchhoff's first law to determine the value of the current at each junction in the circuit. Finally, use Kirchhoff's second law to calculate the voltage drops and solve for the current using Ohm's law.

4. Can Kirchhoff's laws be used to determine the direction of the current?

Yes, Kirchhoff's laws can determine the direction of the current in a circuit. According to Kirchhoff's first law, the total current entering a junction must equal the total current leaving the junction. By labeling the direction of the current in the circuit diagram and applying Kirchhoff's first law, you can determine the direction of the current at each junction.

5. Are there any limitations to using Kirchhoff's laws to deduce the value and direction of the current?

Yes, there are limitations to using Kirchhoff's laws. These laws assume that the circuit is in a steady state and that there are no changing magnetic fields. Additionally, they only apply to circuits with resistors, capacitors, and inductors, and may not be accurate for circuits with non-linear components or high-frequency signals.

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