Ohm's Law

The Fundamental Law

Ohm's Law describes the relationship between voltage, current, and resistance:

V = I × R

Where:

• V = Voltage (Volts)
• I = Current (Amps)
• R = Resistance (Ohms)

Visual Explanation

Understanding Ohm's Law is easier with a visual representation:

The Ohm's Law triangle shows the relationship: Voltage = Current × Resistance

Using the Formula

Find Voltage

V = I × R
V = 2A × 10Ω = 20V

Find Current

I = V / R
I = 12V / 4Ω = 3A

Find Resistance

R = V / I
R = 9V / 3A = 3Ω

Triangle Method

Many people use a triangle to remember:

    V
   ---
  |   |
 I × R |

Cover the value you need, the remaining values show the formula.

Example: LED Circuit

You have a 9V battery and want to power an LED that needs 20mA at 2V.

# Calculate resistor needed
LED_voltage = 2
battery_voltage = 9
current = 0.02  # 20mA
voltage_across_resistor = battery_voltage - LED_voltage
resistance = voltage_across_resistor / current
print(f"Resistor needed: {resistance} Ω")
Output: 350Ω (use 330Ω or 470Ω standard value)

Summary

• V = I × R - The fundamental electronics formula
• Cover what you need to find in the triangle
• Use it to calculate components for any circuit

Next Lesson

In the next lesson, you'll learn about resistors and how to read their color codes.