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Understanding Ohm's Law
ElectronicsThe fundamental relationship between voltage, current, and resistance explained.
What is Ohm's Law?
Ohm's Law is one of the most fundamental principles in electrical engineering. Named after German physicist Georg Simon Ohm, it describes the relationship between voltage (V), current (I), and resistance (R) in an electrical circuit.
V = I × R
V
Voltage
Voltage
I
Current
Current
R
Resistance
Resistance
The Formula
V = I × R
Voltage = Current × Resistance
Understanding the Variables
| Symbol | Name | Unit | Description |
|---|---|---|---|
| V | Voltage | Volts (V) | The electrical "pressure" pushing electrons through a circuit |
| I | Current | Amperes (A) | The flow rate of electrons through the circuit |
| R | Resistance | Ohms (Ω) | How much the circuit opposes the flow of current |
Rearranged Formulas
- Find Current: I = V / R
- Find Resistance: R = V / I
- Find Voltage: V = I × R
Practical Examples
Example 1: LED Circuit
You have a 9V battery and want to power an LED that needs 20mA (0.02A). What resistor do you need?
R = V / I = 9V / 0.02A = 450Ω
Use a 470Ω resistor (nearest standard value)
Example 2: Household Circuit
A 100W light bulb on a 120V circuit draws how much current?
P = V × I, so I = P / V = 100W / 120V = 0.83A