Ohm's Law Explained
Ohm's Law is one of the most fundamental principles in electronics. It defines the relationship between voltage, current, and resistance. Understanding and applying Ohm's Law is essential for anyone working with electrical circuits, whether you're a hobbyist, student, or professional.
What is Ohm's Law?
Ohm's Law states that the current (I) flowing through a conductor between two points is directly proportional to the voltage (V) across the two points and inversely proportional to the resistance (R) of the conductor.
The basic formula is:
This can also be rearranged as:
- I = V / R
- R = V / I
Understanding the Units
Before diving into practical examples, it’s important to understand the units involved:
- Voltage (V): Measured in volts (V)
- Current (I): Measured in amperes (A)
- Resistance (R): Measured in ohms (Ω)
Visualizing Ohm's Law
A helpful way to visualize Ohm's Law is with the triangle method:
V at the top of the triangle, with I and R below. Cover the variable you want to solve for:
- Cover V: I × R
- Cover I: V / R
- Cover R: V / I
Real World Example #1: Finding Current
You have a 9V battery connected to a resistor of 3Ω. How much current flows through the circuit?
Real World Example #2: Finding Resistance
A circuit uses a 5V power supply and draws 0.5A of current. What is the resistance?
Real World Example #3: Finding Voltage
A device has a resistance of 100Ω and uses 0.02A of current. What voltage does it need?
Why Ohm's Law is Important
- Helps you choose appropriate resistors and power supplies
- Prevents damage by estimating how much current a component will draw
- Used in designing circuits to meet specific performance goals
Common Mistakes to Avoid
- Not using consistent units (e.g., milliamps vs amps)
- Confusing voltage drop with supply voltage
- Overlooking resistance in wires and connections in high-current applications
Applications in the Real World
- LED Circuits: Calculating correct resistor to avoid burning out the LED
- Amplifiers: Setting input and feedback resistors for desired gain
- Power Supply Design: Estimating load current and required voltage regulation
Practice Problems
Problem 1: A resistor has a resistance of 10Ω, and a current of 2A flows through it. What is the voltage across the resistor?
Problem 2: If the voltage across a resistor is 9V and the current is 3A, what is the resistance?
Problem 3: A 100Ω resistor is connected across a 12V battery. How much current flows through it?
Conclusion
Ohm’s Law is simple but powerful. With a solid understanding of voltage, current, and resistance relationships, you'll be well-equipped to analyze and build circuits effectively. Keep practicing with real-world examples and tools like our calculators to build intuition over time.