Ohm’s law is a fundamental principle of electrical engineering that describes the relationship between the current flowing through a conductor and the voltage applied to it. It states that the current flowing through a conductor is directly proportional to the voltage applied to it, provided the temperature and other physical factors remain constant. This principle was discovered by German physicist Georg Simon Ohm in the early 19th century and has since become a cornerstone of electrical engineering and physics.

History

Georg Simon Ohm (1789-1854) was a German physicist and mathematician who is best known for Ohm’s law, which he first described in 1827. Ohm was born in Erlangen, Germany, and initially studied theology before becoming interested in science and mathematics. After completing his education, he taught mathematics and physics in several German universities before being appointed professor of physics at the University of Munich in 1852. Ohm’s work on electrical circuits, including his famous law, paved the way for the development of modern electrical engineering and electronics. Today, he is widely regarded as one of the most important figures in the history of electrical science, and his name lives on in the unit of electrical resistance, the ohm (Ω).

The Formula

The formula for Ohm’s law is typically written as:

I = V/R

Where I is the current flowing through the conductor in amperes, V is the voltage applied to the conductor in volts, and R is the resistance of the conductor in ohms. This formula shows that the current through a conductor is directly proportional to the voltage across it, and inversely proportional to the resistance of the conductor.

To understand Ohm’s law in more detail, it is helpful to break down the key components of the formula and how they relate to one another.

Current

Current is the flow of electric charge through a conductor, typically measured in amperes (A). In a simple circuit, current flows from the positive terminal of a voltage source, through the circuit components, and back to the negative terminal of the source. The amount of current that flows through the circuit is determined by the voltage applied to it and the resistance of the circuit.

Voltage

Voltage, or electric potential difference, is the measure of the potential energy per unit of charge in an electrical circuit. It is typically measured in volts (V) and represents the amount of work that must be done to move a unit of electric charge from one point to another in the circuit. Voltage is often compared to the pressure in a water pipe, with higher voltage levels indicating a greater potential energy difference.

Resistance

Resistance is a measure of how much a material or component opposes the flow of electric current. It is typically measured in ohms (Ω) and can be thought of as the amount of friction or resistance that the electric charge encounters as it flows through the circuit. Materials with high resistance, such as rubber or glass, are known as insulators, while materials with low resistance, such as copper or aluminum, are known as conductors.

Now that we have a basic understanding of the components of Ohm’s law, let’s examine how they interact with one another using a few examples.

Example 1:

Suppose we have a circuit with a voltage source of 12 volts and a resistor with a resistance of 6 ohms. What is the current flowing through the circuit?

Using Ohm’s law, we can calculate the current as:

I = V/R = 12/6 = 2 amperes

This tells us that 2 amperes of current will flow through the circuit when a voltage of 12 volts is applied across a resistor with a resistance of 6 ohms.

Example 2:

Now suppose we keep the voltage source at 12 volts, but increase the resistance of the circuit to 12 ohms. What is the new current flowing through the circuit?

Using Ohm’s law again, we can calculate the new current as:

I = V/R = 12/12 = 1 ampere

This tells us that when the resistance of the circuit is doubled, the current flowing through it is halved.

Example 3:

Finally, suppose we keep the resistance of the circuit at 6 ohms, but increase the voltage source to 24 volts. What is the new current flowing through the circuit?

Once again using Ohm’s law, we can calculate the new current as:

I = V/R = 24/6 = 4 amperes

This tells us that when the voltage applied to the circuit is doubled, the current flowing through it doubles.

The following link is for an interactive simulation from the University of Colorado for Ohms Law. Ohms Law Simulation.

Power

Power is another important concept in electrical engineering and is closely related to Ohm’s law. Power is the rate at which energy is transferred or converted from one form to another, typically measured in watts (W). In the context of electrical circuits, power is the rate at which electric energy is converted into another form of energy, such as heat or light.

The formula for calculating power is:

P = VI

Where P is the power in watts, V is the voltage in volts, and I is the current in amperes. This formula shows that power is directly proportional to both voltage and current. Alternatively, power can also be expressed as:

P = I^2R

Where R is the resistance of the circuit in ohms. This formula shows that power is proportional to the square of the current and inversely proportional to the resistance of the circuit.

Understanding power is important for a variety of reasons. For example, knowing the power rating of a device can help determine whether it is appropriate for a particular application or whether additional components, such as a heat sink or cooling fan, may be required. Additionally, understanding the power consumption of a circuit can help estimate its operating costs and optimize its energy efficiency.

It is also important to note that electrical power can be either AC (alternating current) or DC (direct current), and the way power is calculated for each type of current is different. For AC circuits, the concept of power factor is also important, as it reflects how efficiently the circuit is converting electrical energy into other forms of energy.

Overall, understanding power is essential for anyone working with electrical circuits, and it is closely related to other fundamental concepts such as voltage, current, and resistance.

In conclusion

Ohm’s law is a fundamental principle in electrical engineering that describes the relationship between voltage, current, and resistance in a circuit. By understanding this law, engineers and technicians can design, analyze, and troubleshoot a wide range of electrical systems, from simple circuits to complex industrial machinery. Additionally, Ohm’s law serves as a foundation for other important concepts in electrical engineering, such as power, energy, and efficiency. Whether you are a student just starting to learn about electricity or a seasoned professional, a solid understanding of Ohm’s law is essential for success in this field.