The discussion of material about electrical circuits in physics cannot be separated from Kirchoff’s law. The sound of Kirchhoff’s law basically describes a simple electrical circuit which consists of battery, interconnected lights and switches.
In order to help friends find references to learn the concept of Kirchhoff law material 1 and 2, here we review the understanding, sound of the law, formulas and also examples of questions and complete discussions. For more details, please read the article below.
Understanding Kirchhoff’s Law
Via : www.sciencefacts.net
Kirchhoff’s law is a law that governs branching and loops. Kirchhoff’s law was discovered and first introduced by Gustav Robert Kirchhoff, a physicist from Germany in 1845.
This law describes current and voltage or potential difference. Basically, this law describes a simple electrical circuit consisting only of interconnected switches, batteries and lamps.
When the switch is opened, the electric current has not flowed so that the lamp remains in a state of extinguishment. Then, when the switch is connected, then the electric current will flow until it makes the lights turn on.
This law has an important role in electronic circuit, among the advantages and functions of Kirchhoff’s law is to make the calculation of unknown voltages and currents easy and also The analysis and simplification of complex closed-loop circuits becomes easy to manage.
Kirchhoff’s law works on the assumption that no magnetic field fluctuates in a closed loop. Electric fields and electromotive forces can be induced which results in a violation of Kirchhoff’s rule under the influence of varying magnetic fields.
Differences between Kirchhoff’s Law 1 (Current) and Kirchhoff’s Law 2 (Voltage):
| KCL | KVL |
| The sum of all currents going to a given node is equal to the sum of all currents going out of that node | The sum of all voltages around a closed path (loop) is zero |
| Node analysis takes precedence to obtain node potential because incoming/outgoing currents can be expressed in node potential. | Loop analysis takes precedence to obtain loop currents because loop potential differences can be expressed in loop currents |
Kirchoff’s Law Limitations:
Kirchhoff’s law has limitations that apply only to all cases where the total electric charge is constant in the region under consideration as long as the law is applied to a given point.
However, in some cases, the charge density may not be constant. Since the charge is conserved, the only way this is possible is if there is a flow of charge across the territorial boundary. This flow will produce current/Power, thus violating Kirchhoff’s law.
Another limitation of Kirchoff’s law is that circuits work under the assumption that there is no fluctuating magnetic field in a closed loop. Electric fields and GGL can be induced, which causes Kirchhoff’s law to break in the presence of a variable magnetic field.
Kirchhoff’s Law 1
“The sound of Kirchhoff’s law 1 states that the magnitude of the strength of the current entering the branching is equal to the magnitude of the strength of the outgoing current or the amount of strong current at a point is equal to zero.”
From the sound of the law, it can be concluded that the total charge going to a point is equal to the total charge coming out of that point. If mathematically formulated the formula of Kirchhoff’s law is:
Kirchhoff’s law is still further divided into 2 based on its rules. The first is Kirchhoff’s Law 1 which discusses charge, and Kirchhoff’s Law 2 which focuses more on discussing potential differences in closed circuits. Here is the formula for Kirchhoff’s law 1:
Formula of Kirchhoff’s Law 1
The formula of Kirchhoff’s law 1 states that the amount (sigma) of incoming current has a value equal to the amount of outflow (Σ I in = Σ Iout), so in mathematical equations it is denoted I1 + I3 + I4 = I2 + I5
In an electric circuit, current strength is the amount of charge flowing on the electrically conducting component in a certain period of time, meaning that electric charge is conserved.
From the statement above, the amount of electric charge entering and leaving the branching point always has the same value, so the kirchhoff formula 1 can also be notated: Q1 + Q3 + Q4 = Q2 + Q3
The term node in an electrical circuit generally refers to the connection or junction of two or more current-carrying lines or elements such as wires and components.
Then in order for current to flow in or out of the node, a closed circuit path must be present. We can use the formula of Kirchhoff’s law 1 above when we want to analyze parallel circuits.
Examples of Kirchhoff Law Problems 1
After understanding the basic concepts of Kirchhoff’s Law theory 1 & 2 above, now you can apply them in the example problem. Here are some examples of Kirchhoff’s law.
- Take a look at the picture of the electrical circuit below! If R1 = 2Ω, R2 = 4Ω, R3 = 6Ω, what is the magnitude of the strong electric current flowing?
Discussion:
# Step 1: Determine the direction of the current in the circuit (in this example we use the direction of the current clockwise). When current flows across the resistor, there is a potential decrease, so the equation V = IR is negatively signed.
# Step 2: If the current moves from low to high then the source of emf (E) is marked positive, Likewise, if the current moves from high voltage to low (+ to -) then the source of emf (E) is marked negative, so the equation is obtained: – IR1 + E1 – IR2 – IR3 – E2 = 0
# Step 3: Substitute the value into the equation that has been obtained above:
–2I + 10 – 4I – 6I – 5 = 0
-12I + 5 = 0
I = -5/-12
I = 0.416
So the electric current flowing in the circuit is 0.416 A.
- From the following figure of the electric circuit, it is known that the electric current passing through I2= 1A, I1= 3A, I4= 0.5A. Then determine how much electric current passes through I3 and I5!
Via : Quipper.com
Discussion:
This question can be solved by applying Kirchoff’s law 1 where:
∑i in = ∑Vi in
I1 = I5
I2+I3+I4 =I5
1 + I3 + 0.5 = 3
I3 = 3 – 0.5
I3 = 1.5A
So the magnitude of the strong electric current passing through I3 is 1.5 A and passing through I5 is 3 A.
Kirchoff’s Law 2
Kirchoff’s Law 2
Kirchoff’s Law 2 states that in a loop circuit , the algebraic sum of GGL and the number of its potential decreases are equal to zero. Or it can also sound that the potential difference or voltage in a closed circuit is equal to zero.
Unlike Kiirchoff I’s law which applies to branched electrical circuits, Kirchoff’s law 2 applies and is used in closed circuits to analyze potential or voltage differences. Therefore, this law is also called Kirchoff’s voltage law.
Formula of Kirchhoff’s Law 2
The formula of kirchhoff’s law 2 is ∑V+∑(I⋅R)=0. To illustrate, if we have a charge (Q) at any potential difference point (V), then the energy possessed by that charge is QV.
Then if the charge is discharged (moving), then the charge owned will gain additional energy or lose some energy when passing through battery resistors or other circuit elements. But when the charge returns to the starting point, the energy will return to QV.
The number of closed circuits in one electrical circuit is not only 1 or it can even be two or more. In its application to closed circuits, there are rules that must be observed:
- Define the loop of each circuit in a specific direction.
- When in the direction of the loop, the voltage drop is given a plus sign (+) and vice versa if it is opposite to the loop, the voltage drop is marked negative (-).
- If when following the direction of the loop, the voltage source is met first with the positive pole, then GGL will be marked positive. Vice versa if what is encountered first is the negative pole, then GGL also has a negative sign (-).
When an AC electrical circuit or DC circuit is analyzed based on Kirchhoff circuit law 2, you should be clear with all the terminology and definitions that describe circuit components such as paths, vertices, meshes, and loops.
Examples of Kirchhoff’s Law 2
- Take a look at the picture of the electrical circuit below. Find the current flowing on a 40Ω, R3 Resistor!
Via : electronics-tutorials.ws
Discussion:
# Step 1: The circuit has 3 branches, 2 nodes (A and B) and 2 independent loops. So the equation is obtained:
- Node A: I1 + I2 = I3
- Node B : I3 = I1 + I2
# Step 2: Using Kirchhoff’s Law of Voltage, we get the following KVL equation:
- They will perpute arus 1 : 10 = R 1 I1 + R3 I3 = 10I1 + 40I3
- They will perpute arus 2 : 20 = R 2 I2 + R3 I3 = 20I2 + 40I3
- Current rotation 3 : 10 – 20 = 10I1 – 20I2
# Step 3: Since I3 is the sum ofI1 + I2, the following equation is obtained:
- Persamaan 1 : 10 = 10I1 + 40(I1 + I2) = 50I1 + 40I2
- Persamaan 2 : 20 = 20I 2 + 40(I1 + I2) = 40I1 + 60I2
# Step 4: From the two results above, we have obtained two “Simultaneous Equations” that can be simplified:
- Substitution of value I1 to I2 = -0.143 Amps
- Substitution of the value of I2 to I1 = +0,429 Amps
# Step 5: Since I3 = I1 + I2, then:
- The current flowing in resistor R3 is -0.143 + 0.429 = 0.286 Amps
- The voltage across resistor R3 is 0.286 x 40 = 11.44 volts
Application of Kirchhoff’s Law
Just like other laws in physics, Kirchoff’s law is also applied in everyday life. However, examples of its application may be quite difficult to see with the naked eye because it is a formula, not a component.
After knowing the sound of Kirchoff’s law as described above, the next is how it applies:
- Assume allteganganandObstaclesGiven. (V1, V2,… R1, R2, etc.)
- Setelectric currentwhich flows into each branch (clockwise or counterclockwise)
- Label each branch with branch currents. ( I1, I2, I3 etc.)
- Find the equation of Kirchoff’s first law for each vertice.
- Find the equation of Kirchoff’s second law for each independent loop of the circuit.
- Use the simultaneous linear equations necessary to find the unknown electric current.
Examples of the application of Kirchhoff’s law in everyday life that can certainly be seen are inelectrical circuit, Whether it is parallel or series. For example, when the electrical circuit is arranged in series, the lamp installed closest to the power source has a brighter flame.
Meanwhile, when arranged in parallel, all lights installed have almost the same bright intensity, even though the distance from the power source is different.
Conclusion:
Kirchhoff’s law states that the total current at a junction is equal to the sum of currents outside the junction, while the amount of voltage around a closed loop is equal to zero.
Also Read: Ohm’s Law
Well, that was the explanation from the electronic wiki about Kirchhoff’s law, starting from the sound of Kirchhoff’s law, application formulas and example problems. From the explanation above, hopefully it can help make it easier for you to work on various types of examples of kirchoff law problems, both kirchoff law 1 questions and examples of kirchhoff law 2 questions.
