# Ohm’s Law Explained: How Voltage, Current & Resistance Work

Welcome to our latest tutorial dedicated to the cornerstone of circuit design and electronics: Ohm’s Law. Whether you’re interested in tinkering with hobby electronics, getting creative with motorized props and animatronics or building robots, mastering Ohm’s Law is crucial. It’s the guiding principle that drives the relationship between voltage, current, and resistance within every electrical circuit you will build. This is one of the few formulas in electronics that you’ll use on a regular basis so we’re going to dive deep into how it works and how to use Ohm’s Law to ensure your circuits are designed correctly, perform efficiently, and operate safely. No matter if you’re a seasoned maker or a curious beginner, this practical guide will empower you to bring your electronic projects to life with confidence and precision. So grab a calculator and prepare to explore a formula that’s at the heart of electronics …plus I’ll also show you an easy way to remember it!

## What is Ohm’s Law?

Ohm’s Law is a fundamental concept in electrical engineering and physics that describes the relationship between current, voltage, and resistance in an electrical circuit. It was named after the German physicist Georg Simon Ohm. He first formulated the law and published his findings in 1827 in a book titled “Die galvanische Kette, mathematisch bearbeitet” or “The Galvanic Circuit Investigated Mathematically.”

Ohm’s work laid the foundation for much of our modern understanding of electricity, and the unit of electrical resistance, the ohm, was named in his honor. His law, Ohm’s Law, has become a fundamental principle in electrical engineering and physics, describing the relationship between current, voltage, and resistance in an electrical circuit, which states V = I x R. This equation tells us that the voltage across a resistor, for instance, is equal to the current flowing through the resistor multiplied by the resistance of the resistor.

Here’s a brief overview of what each term means and how they interact:

• Voltage (V): This is the force that pushes the charge through the circuit, also called “electrical pressure.” It’s a measure of potential energy that’s typically provided by a power supply such as a battery or generator. The unit of voltage is the volt (V).
• Current (I): This is the flow of electric charge in the circuit. The direction of current is conventionally considered as the direction in which positive charges would flow. This flow is driven by the voltage supplied. The unit of current is the ampere (A).
• Resistance (R): This is a property that impedes the flow of current. Think of it like friction against the movement of electrons. The higher the resistance, the less current will flow for a given voltage. The unit of resistance is the ohm (Ω).

In a basic circuit:

• Increasing the voltage will increase the current, assuming the resistance stays the same. This is because the greater “pressure” pushes more electrons to flow.
• Increasing the resistance will decrease the current, assuming the voltage stays the same. This is because more resistance makes it harder for the electrons to flow.
• Current can also be seen as the result of voltage divided by resistance (I = V/R). So, for a fixed voltage, the current decreases as the resistance increases, and vice versa. Similarly, for a fixed resistance, the current increases as the voltage increases, and vice versa.

Remember, this is a simplification and actual circuits can be more complicated, with components like capacitors, inductors, diodes, and transistors which behave differently. But for simple, direct current (DC) circuits with resistive elements, Ohm’s Law provides a basic and helpful analysis.

As an electronics hobbyist or professional, motorized prop-maker, roboticist, and/or animatronics builder, you’ll often use Ohm’s Law in a variety of scenarios during the design, construction, and troubleshooting of your projects. Here are a few examples:

• Choosing components: You might use Ohm’s Law to calculate the appropriate resistance for a resistor to limit current to an LED or other component, based on the component’s rated voltage and current.
• Power calculations: Combined with the power equation P=IV (Power equals current times voltage), you can use Ohm’s Law to calculate the power requirements of a circuit or individual components, which is critical when selecting power supplies, batteries, or designing power distribution systems.
• Designing motor circuits: You can use Ohm’s Law to understand how much current a motor will draw at a given voltage and resistance, which is important for selecting appropriate motor controllers and power sources.
• Building power supplies: When designing voltage dividers or using voltage regulators, Ohm’s Law can help determine the values of the resistors to use.
• Troubleshooting: If a component in a circuit is not behaving as expected, you can use Ohm’s Law to help diagnose the problem. For instance, if a component is getting too hot, it might be because too much current is flowing through it.
• Protection circuits: Designing circuits with components like fuses or circuit breakers, which are meant to protect devices from current overloads, often requires a solid understanding of Ohm’s Law.

In each of these cases, Ohm’s Law is a fundamental tool that helps you understand the relationship between voltage, current, and resistance in your circuits, and allows you to design and construct safe and effective devices.

## Ohm’s Law Triangle Technique

Rather than having to memorize yet another formula, the Ohm’s Law triangle is a simple visual tool that’s often used to help remember the relationships between voltage (V), current (I), and resistance (R) as described by Ohm’s Law. The triangle is set up as follows:

• Voltage (V) is at the top of the triangle
• Current (I) and Resistance (R) are in the bottom corners of the triangle

The triangle can then be used to derive any of the three forms of Ohm’s Law.

## Calculating Voltage: V = IR

Let’s say you know your circuit or component draws a current of 250 mA (I) and has a resistance of 47 Ohms (R). To find Voltage (V), you cover up V in the triangle, leaving I and R. This means V = I x R, which is the standard form of Ohm’s Law. Remember to use the correct units of measurement when using the Ohm’s Law formula. Smaller electronics components typically specify their current ratings in mA (milliamps) rather than in Amps like the formula requires. In this example, 250 mA is equal to .25 A.

To find Voltage (V), you cover up V in the triangle, leaving I and R. This means V = I x R, which is the standard form of Ohm’s Law. Plugging this information into the formula (V = IR) to calculate for volts looks like this:

V = .25 x 10,000 = 11.75 Volts

This means you would need a power supply that can provide 11.75 volts (and at least 250mA) in order for the component(s) in your circuit to work properly.

## Calculating Current: I = V / R

In this example, your circuit or component requires 12V (V) and has a resistance (R) of 68 Ohms. What current will it draw?

To find Current (I), you cover up I, leaving V and R. This gives I = V / R. Plugging this information into the formula (I = V / R) to calculate for current looks like this:

I = 12 / 68 = .176 A (or 176 mA)

This means you would need a power supply that can provide 12 volts and at least .176 A in order for the component(s) in your circuit to work properly.

## Calculating Resistance: R = V / I

In this example, your circuit or component requires 2V (V) and has a current draw of 20mA. What is the resistance?

To find Resistance (R), you cover up R, leaving V and I. This gives R = V / I.

Plugging this information into the formula (R = V / I) to calculate for resistance looks like this:

R = 2 / .02 = 100 Ohms

This means you would need a 100 Ohm resistor in order for the component(s) in your circuit to work properly.

Mastering Ohm’s Law is an essential step on your journey to becoming proficient in building and troubleshooting electronic circuits. The fundamental formula, V = IR, will empower you to not only build circuits correctly but also diagnose and fix any issues that arise with individual components. These troubleshooting exercises foster growth and a deeper understanding when building your own electronic circuits, allowing you to tackle more complex projects with increased confidence. Using Ohm’s Law is more than just understanding the mathematics; it’s about embracing a mindset of curiosity and problem-solving that lies at the very heart of electronics.