Have you thought about bringing your own Arduino, ESP32 or Raspberry Pi ideas to life? A little circuit analysis will certainly help you along! Electronics can seem like pure magic, but with concentration and a little circuit theory, you will be developing one electronics project after another in no time!
So what is circuit analysis? Simply put, a circuit is a path for the flow of electrons. The flow of electrons is considered an electric current. Circuit analysis aims to help us understand how to examine, manipulate, and use these electrons. It is therefore a fundamental tool in electrical engineering. This includes a basic understanding of Ohm’s law and Kirchhoff’s laws.
So what is circuit analysis? Simply put, a circuit is a path for the flow of electrons. The flow of electrons is considered an electric current. Circuit analysis aims to help us understand how to examine, manipulate, and use these electrons. It is therefore a fundamental tool in electrical engineering. This includes a basic understanding of Ohm’s law and Kirchhoff’s laws.
Ohm’s Law
Ohm’s law is explained in detail in this blog, so we cover it only briefly here. We recommend reading that article to get a thorough understanding of Ohm’s law! For now, we will continue with a quick statement of the law.
Ohm’s law is a fundamental principle in physics that defines the relationship between electric current, voltage, and resistance in an electrical circuit.
Ohm’s law states that the current flowing through a conductor between two points is directly proportional to the voltage across those points and inversely proportional to the conductor’s resistance. Mathematically, Ohm’s law can be expressed as shown in figure 1.
Ohm’s law is a fundamental principle in physics that defines the relationship between electric current, voltage, and resistance in an electrical circuit.
Ohm’s law states that the current flowing through a conductor between two points is directly proportional to the voltage across those points and inversely proportional to the conductor’s resistance. Mathematically, Ohm’s law can be expressed as shown in figure 1.
Figure 1: Ohm’s law.
Voltage, V, is measured in volts.
Current, I, is measured in amperes
Resistance, R, is measured in ohms
See figure 2.
Voltage, V, is measured in volts.
Current, I, is measured in amperes
Resistance, R, is measured in ohms
See figure 2.
Figure 2: A table of the units in Ohm’s law.
* This table is an excerpt from the blog about Ohm’s Law. Read that article for a deeper understanding of Ohm’s law!
* This table is an excerpt from the blog about Ohm’s Law. Read that article for a deeper understanding of Ohm’s law!
Kirchhoff’s Laws
Kirchhoff’s laws are two other fundamental principles of circuit analysis. They describe current and voltage respectively in an electrical circuit and are used to analyse and understand its behaviour. We will cover them one at a time below.
1 - KCL
Kirchhoff’s Current Law (KCL)
This law states that the total current entering a node must equal the total current leaving it (the next figure gives an example and explanation of a node). In other words, the algebraic sum of all currents at a node is zero when entering and leaving currents have opposite signs.
This law states that the total current entering a node must equal the total current leaving it (the next figure gives an example and explanation of a node). In other words, the algebraic sum of all currents at a node is zero when entering and leaving currents have opposite signs.
A water analogy is often used to explain this law. The amount of water flowing into a junction equals the amount flowing out. A node is illustrated in figure 3.
Figure 3: Illustration of Kirchhoff’s current law (KCL). The figure shows a section of an electrical circuit. The currents entering the node (red) equal the currents leaving it (blue).
Returning to the water analogy: if the paths of currents I1, I2, I3, I4, and I5 are water pipes, the currents meet at the node. The red currents point towards the node, and the blue currents point away from it. The total water mass in the red flows must equal that in the blue flows. This is the principle of Kirchhoff’s current law (KCL).
2 - KVL
Kirchhoff’s Voltage Law (KVL)
This law states that the total voltage around any closed loop in a circuit must be zero. A closed loop is a path in an electrical circuit that starts and ends at the same point.
In other words, the sum of all voltage drops in a closed loop equals the total voltage rise in that loop.
This law states that the total voltage around any closed loop in a circuit must be zero. A closed loop is a path in an electrical circuit that starts and ends at the same point.
In other words, the sum of all voltage drops in a closed loop equals the total voltage rise in that loop.
Figure 4: A circuit with a voltage source, V1, and 2 resistors (the zigzag symbols indicate R1 and R2). It forms a closed loop, starting and ending at the same point, V1. The value and direction of current I around the circuit are shown in the centre of the figure.
Figure 4 illustrates how the voltage drop around the closed loop equals the starting voltage applied by source V1. The voltage along the red part of the circuit is the original 9 V from V1. The green part is at 5.4 V, and the blue section is at 0 V.
Let us apply Ohm’s law to each section of the circuit using the values defined in figure 5. The three sections are separated by voltage drops V2 and V3. We calculate V2 and V3, and their sum should be 9 V. This is the concept behind Kirchhoff’s voltage law (KVL).
Figure 5: Calculating the voltage drops in the circuit shown in figure 4
- In figure 5, we first define the circuit values
- Then we calculate voltages V2 and V3
- Finally, we add V2 and V3
This demonstrates Kirchhoff’s voltage law (KVL).
Together, Ohm’s law and Kirchhoff’s laws provide an effective set of tools for analysing electrical circuits and form the basis of several circuit analysis methods. After reading this article, you are one step closer to bringing your electronics dreams and projects to life. We now understand circuit analysis better. Although we have covered only some basics, we are ready to improve further and develop a broader understanding of electronics.
Electronics is a limitless hobby: you can always improve and there is always more to learn. If you are interested in further circuit analysis, other methods and principles include Thévenin, Norton, mesh analysis, and nodal analysis.
We also have an article about a very useful subcircuit: the voltage divider. Take a look! Voltage dividers are used in countless electronic products and are among the most important subcircuits in electronics.
