Exams
Test Series
Previous Year Papers
Syllabus
Books
Cut Off
Latest Updates
Eligibility
Kirchhoff’s First Law: Learn Formula, Conservation of Charge, Solved Examples
IMPORTANT LINKS
Current Electricity
Kirchhoff’s Laws aid in the design of complex circuits with various electrical components found in everyday life. It also aids in investigating any electrical circuits, such as how much current flows in various sections of an electrical circuit.
Kirchhoff’s laws were named after Gustav Robert Kirchhoff, a German physicist. He also helped to advance our understanding of black body radiation and spectroscopy. In 1845, he found the law for the first time. It is the foundation of network analysis and is typically used in the time and frequency domains of circuits. Kirchhoff’s circuit law is the combination of Kirchhoff’s current law and Kirchhoff’s voltage law. Kirchhoff’s law is another name for Kirchhoff’s first law.
In this Physics article, we will discuss more Kirchhoff’s first law.
Kirchhoff’s First Law
Kirchhoff’s first law states that at any node (junction) in a circuit, the sum of currents passing into that node is equivalent to the total of currents flowing out of that node.
This means that if we think of a node as a water tank, the water flow speed filling the tank is equal to the one emptying it.
Kirchhoff’s first law goes by several names, including Kirchhoff’s Junction Rule, Kirchhoff’s Current Law (KCL), Kirchhoff’s Point Rule, and Kirchhoff’s Nodal Rule. Kirchhoff's first law is based on the law of conservation of charge.
In the case of electricity, the sum of currents entering the node equals the sum of currents exiting the node.
Kirchhoff's First Law Formula
Currents flowing into the point (A) = Currents flowing out of the point (A)
The current that flows into the point and also that flowing out of it have a positive sign (+) at the junction (node).
In a closed circuit, the algebraic sum of currents at the junction equals zero.
The current flowing into the point has a positive sign (+) at the junction (node), whereas the current flowing out of the point does have a negative sign (-).
Kirchhoff’s First Law & Conservation of Charge
Kirchhoff’s first law of electrical circuits is based on conservation of charge, while Kirchhoff’s second law of electrical circuits is based on energy conservation. Kirchhoff’s concept is known as the Conservation of Charge because the current is preserved around the junction with no current loss.
Since the electric current intensity in (Amperes) corresponds to the number of electric charges in (Coulomb) crossing a cross-section area in one second, Kirchhoff’s first law is an application of the principle of conservation of charge (the quantity of charge flowing into a node is equivalent to the amount of charge flowing out of that node).
- 3 Live Test
- 163 Class XI Chapter Tests
- 157 Class XII Chapter Tests
Advantages and Disadvantages Kirchhoff’s Laws
Advantages
Kirchhoff’s laws are applied to determine:
- The current, voltage, and internal resistance values in DC circuits.
- We may also use this law to find the unknown resistance in the circuit.
- Kirchhoff’s laws are used extensively in the construction of Wheatstone Bridge. It’s useful for mesh and node analysis.
Disadvantages
- Kirchhoff’s laws are inapplicable to high-frequency alternating current circuits. Only when the electric charge in a circuit is constant does the current law apply.
- KVL is used under the assumption that magnetic fields in a closed circuit do not change. As a result, we cannot use KVL when the magnetic field fluctuates inside a circuit.
Solved Examples on Kirchhoff’s First Law
Example 1. Find the current
Solution 1. Currents
Substitute the known values
Install the Testbook app right away to take advantage of their comprehensive and dependable study materials, as well as the assistance of Testbook experts, in order to ace one’s desired competitive exam. Take advantage of incredible savings right now by installing the free Testbook app.
Kirchhoffs First Law FAQs
What is Kirchhoff's first law?
Kirchhoff's first law or Kirchhoff's junction rule, states that the sum of currents flowing into any node (junction) in an electrical circuit is equal to the sum of currents flowing out of that node.
Is Kirchhoff's first law applicable to AC circuits?
Yes, Kirchoff’s law is applicable to AC circuits.
What is Kirchhoff's current law formula?
What is the significance of Kirchhoff's first law?
Kirchhoff's first law expresses the conservation of charges.
What is Kirchhoff's current law and voltage law?
The analysis of lumped parameter circuits is based on Kirchhoff's current law and Kirchhoff's voltage law. These rules, combined with the voltage-current characteristics of the system's circuit parts, allow us to do a systematic analysis of any electrical network.
Explain the sign convention of Kirchhoff's first law?
Currents flowing into a node are taken as positive whereas, currents flowing out of a node are taken as negative.