Understanding how current flows through a resistor is a basic — but essential — part of learning electronics. As a student, hobbyist, or tinkerer 🛠️, knowing how to calculate current helps you build and troubleshoot circuits with confidence.
Let’s break it down in a simple way.
Table of Contents
⚡ What Is Current?
Current is the flow of electric charge in a circuit. It’s measured in amperes (A) and is what powers your devices — from tiny LEDs to massive motors!
The amount of current depends on two main things:
- The voltage across the resistor
- The resistance of the resistor
🧮 The Formula: Ohm’s Law
To calculate the current in a resistor, we use Ohm’s Law:
I = V / RWhere:
- I = current (in amperes)
- V = voltage across the resistor (in volts)
- R = resistance (in ohms)
This formula tells us how current depends directly on voltage and inversely on resistance.
🔌 Example Calculation
Let’s say:
- Voltage (V) = 9 volts
- Resistance (R) = 3 ohms
I = V / R
I = 9 / 3 = 3 ASo, the current flowing through the resistor is 3 amperes.
📌 Why It’s Important
- Helps you choose the right resistor value
- Prevents overheating or burning components
- Essential for designing efficient circuits
- Makes troubleshooting faster and safer
💡 Quick Tips
- Use a multimeter to measure voltage and resistance directly
- Always check your units: volts (V), ohms (Ω), amps (A)
- For series circuits, current is the same through all resistors
- In parallel circuits, calculate voltage across each resistor separately