Resistors are one of the most fundamental components in electronics, playing a crucial role in controlling the flow of electric current within a circuit. By providing resistance—measured in ohms (Ω)—they limit the amount of current that can pass through, protect sensitive components, divide voltages, and shape signal behavior. Whether you’re powering an LED, designing a voltage regulator, or building complex circuits, resistors are essential tools in shaping how electricity behaves. Understanding how they work and how to select the right type is a key first step in mastering basic electronics.
Ohm’s Law
Ohm’s Law is a fundamental principle in electronics that defines the relationship between voltage, current, and resistance in an electrical circuit. Formulated by German physicist Georg Simon Ohm in the 1820s, this law provides a simple but powerful equation:
V = I × R
Where:
- V is voltage in volts (V)
- I is current in amperes (A)
- R is resistance in ohms (Ω)
Understanding the Equation
This equation tells us that the voltage across a resistor is directly proportional to the current flowing through it, multiplied by the resistance. If you know any two of the three variables (voltage, current, resistance), you can calculate the third:
- To find voltage: V = I × R
- To find current: I = V ÷ R
- To find resistance: R = V ÷ I
Practical Example
Imagine you connect a resistor with a value of 220 ohms to a 9-volt battery. To find the current flowing through the circuit:
I = V ÷ R = 9V ÷ 220Ω ≈ 0.041A or 41mA
This tells you that 41 milliamps of current will flow through the resistor.
Why It Matters
Ohm’s Law is essential for designing and analyzing circuits. It helps you:
- Choose the right resistor to protect LEDs and components
- Determine power consumption
- Troubleshoot circuit issues
- Understand how changing one value affects others
In short, Ohm’s Law is a foundational tool for anyone working with electricity, from beginners wiring their first LED to engineers designing complex systems.
Power Consumption & Dissipation
In electronics, power refers to the rate at which energy is consumed or converted within a circuit, and it’s measured in watts (W). When current flows through a resistor, electrical energy is converted into heat—this is known as power dissipation. The power dissipated by a resistor can be calculated using the formula:
P = V × I
where P is power in watts, V is voltage across the resistor, and I is the current through it. Since Ohm’s Law relates voltage, current, and resistance, the formula can also be expressed as:
P = I^2 × R or P = V^2 ÷ R
These variations allow you to compute power using whichever values you have. Understanding power dissipation is essential for selecting resistors with appropriate wattage ratings to prevent overheating and component failure.
Moving on to real-world use cases
Now that we’ve covered the basics of resistors, Ohm’s Law, and power dissipation, it’s time to explore how these concepts apply in real-world circuits. From limiting current to safely power an LED, to creating voltage dividers and setting bias points in amplifiers, resistors are used in countless practical ways. By working through a few simple examples, you’ll see how to choose the right resistor values, calculate power requirements, and apply theory to hands-on projects—building the foundational skills needed to design and troubleshoot electronic circuits with confidence.
…More on practical applications next week.