The Relationship Between Voltage, Current and Resistance

Voltage (V), Current (I) and Resistance (R) are directly related by Ohm's Law.

If you know any two of these quantities, you can calculate the third.

The Ohm's Law Triangle

      V
────────
I      R

The triangle places:

• Voltage (V) at the top.
• Current (I) at the lower left.
• Resistance (R) at the lower right.

How to Use the Triangle

Simply cover the quantity you want to calculate.

This method allows you to derive the correct equation in just a few seconds.

Example 1 – Calculate Current

Supply Voltage = 24 V

Resistance = 12 Ω

Cover I in the triangle.

Formula:

I = V ÷ R

Calculation:

I = 24 ÷ 12 = 2 A

Example 2 – Calculate Voltage

Current = 0.5 A

Resistance = 100 Ω

Cover V.

Formula:

V = I × R

V = 0.5 × 100 = 50 V

Example 3 – Calculate Resistance

Voltage = 12 V

Current = 0.25 A

Cover R.

Formula:

R = V ÷ I

R = 12 ÷ 0.25 = 48 Ω

Why the Triangle Works

The triangle is simply a visual representation of Ohm's Law.

It helps students remember the correct mathematical relationship without having to memorise three separate equations.

Although experienced engineers usually remember the formulas directly, the triangle remains a useful learning tool for beginners.

When to Use the Triangle

• Solving homework problems.
• Designing electronic circuits.
• Choosing resistor values.
• Troubleshooting electrical equipment.
• Calculating LED resistors.
• Checking power supply circuits.

Common Mistakes

• Using volts instead of millivolts incorrectly.
• Mixing amperes and milliamperes.
• Using resistance in kilo-ohms without converting units.
• Choosing the wrong equation.
• Ignoring unit conversions.

Quick Practice

Answers

• 30 mA
• 30 V
• 8 Ω
• 22.7 mA

Key Points

• The Ohm's Law Triangle is a memory aid.
• Place Voltage at the top of the triangle.
• Current is at the lower left.
• Resistance is at the lower right.
• Cover the unknown quantity to reveal the correct formula.
• Always use consistent units when performing calculations.