OhmsLaw

Ohm’s Law

Ohm’s Law is one of the most important rules in electronics. It describes how voltage, current, and resistance are connected in any electrical circuit. Whether you are adding an LED to a breadboard or trying to figure out why a motor is stalling, Ohm’s Law explains what is happening.

Why does this matter?

Every wire, battery, sensor, and motor in your robot follows Ohm’s Law. Understanding it helps you predict how your circuit will behave — and helps you fix problems when something goes wrong.

The Three Key Ideas

The best way to understand these three ideas is to imagine electricity flowing through a water pipe:

• Voltage (V) — Measured in Volts. Voltage is like the water pressure in the pipe. It is the force that pushes electricity through the circuit. Higher voltage means a stronger push, which allows electricity to do more work.

• Resistance (R) — Measured in Ohms (Ω). Resistance is like a kink or squeeze in the pipe. It fights against the flow of electricity, slowing it down. Every wire, component, and material has some resistance.

• Current (I) — Measured in Amps (A). Current is like the amount of water actually flowing through the pipe. It is the rate at which electricity moves through the circuit.

The Equation

Ohm’s Law says that these three values are always connected by one simple formula:

Where:

• $V$ is voltage (Volts)
• $I$ is current (Amps)
• $R$ is resistance (Ohms)

Using basic algebra, you can rearrange this to solve for any of the three values:

• $V = I \times R$ — Find voltage if you know current and resistance
• $I = V / R$ — Find current if you know voltage and resistance
• $R = V / I$ — Find resistance if you know voltage and current

How the Values Affect Each Other

Because this is a ratio, changing one value always affects the others:

• If Voltage goes up (and Resistance stays the same): The push gets stronger, so more current flows. Think of turning up the water pressure — more water flows through the pipe.
• If Resistance goes up (and Voltage stays the same): The path gets more restricted, so less current flows. Think of squeezing the pipe tighter — less water gets through.

A Real Example

Say your Arduino outputs 5V and you want to safely light up an LED. A typical LED needs about 20mA (0.02A) of current. Using Ohm’s Law, you can figure out what size resistor you need:

So you would pick a resistor close to 250 Ohms to protect the LED!