Ohm’s Law is one of the cornerstones of electrical engineering. It defines the relationship between voltage, current, and resistance in an electric circuit—essential knowledge for designing safe and efficient electrical systems.

A Bit of History: Where Ohm’s Law Comes From

Ohm’s Law was introduced in 1827 by German physicist and mathematician Georg Simon Ohm. In his publication “Die galvanische Kette, mathematisch bearbeitet” (“The Galvanic Circuit Investigated Mathematically”), he stated that the electric current in a circuit is directly proportional to the applied voltage and inversely proportional to the circuit’s resistance. Although his theory was met with skepticism at first, it eventually became a fundamental concept in both electronics and electrical engineering.

The Ohm’s Law Triangle: Know Two, Solve for the Third

If you know any two of these, you can calculate the third using Ohm’s Law.

The Math Behind It

The basic formula is:

V = I × R

Where:

• V is voltage in volts (V)

• I is current in amperes (A)

• R is resistance in ohms (Ω)

From this, you can also derive:

• I = V / R

• R = V / I

Making It Simple: The Water Analogy

Think of electricity like water flowing through a pipe:

• Voltage (V) is like water pressure.

• Current (I) is the actual flow of water.

• Resistance (R) is like the pipe’s width—a narrower pipe (higher resistance) restricts flow.

If you increase pressure (voltage), more water (current) flows—unless the pipe is too narrow, in which case flow is restricted. Electrical circuits work the same way.

Troubleshooting with Ohm’s Law

In system maintenance, Ohm’s Law helps technicians find and fix problems.

• If current is higher than expected, there might be less resistance or excess voltage.

• If current is lower, it might point to increased resistance, possibly from corrosion, poor connections, or damaged components.

Real-World Applications

1. Designing Circuits

Engineers rely on Ohm’s Law to determine proper resistance values so that devices operate safely.

Example:
A 9V battery is used to power an LED that needs 0.02 A. What resistor should you use?

R = V / I = 9 / 0.02 = 450 Ω
→ Use a 450-ohm resistor in series to protect the LED.

2. Electrical Safety

Calculating current helps size the right cables and fuses, preventing overheating or fires.

Example:
An electric stove runs on 220V and has 24 ohms of internal resistance:

I = V / R = 220 / 24 ≈ 9.17 A
→ Use a cable and fuse rated for at least 10A.

3. Troubleshooting and Repairs

Technicians use Ohm’s Law to identify faults.

Example:
If a circuit is supposed to draw 1A but only shows 0.5A, and voltage is correct, the issue could be high resistance due to a bad wire or loose connection.

What Can Affect Ohm’s Law?

Though extremely useful, Ohm’s Law isn’t perfect in all situations. Here’s why:

1. Temperature

Resistance can change with temperature. For example, metal conductors increase resistance when they heat up.

Example:
Incandescent bulbs have much higher resistance when lit than when cold.

2. Non-Ohmic Materials

Some components don’t follow Ohm’s Law. Semiconductors like diodes and transistors don’t have a linear V-I relationship.

Example:
A diode only allows current to flow in one direction, and its resistance changes depending on applied voltage.

Try It Yourself: Ohm’s Law Experiments

To test Ohm’s Law, use a simple setup with:

• A voltage source (like a 9V battery)

• A resistor (e.g., 100 Ω)

• A multimeter

Example:
Connect the resistor to the battery and measure current:

I = V / R = 9 / 100 = 0.09 A (or 90 mA)
The actual reading should be close if everything’s wired correctly.

Final Thoughts

Ohm’s Law is a fundamental tool in the world of electricity. From designing and building circuits to ensuring electrical safety and solving technical issues, this principle is everywhere. While there are limits—especially with temperature changes and non-linear components—it remains essential in every electrical engineer’s toolkit.

Learning and applying Ohm’s Law deepens your understanding of how circuits behave and empowers you to find real-world solutions in both everyday life and complex industrial systems.