Fundamentals ReferenceUpdated 2026-08-15

Ohm's Law: Theory, Formula Wheel, and Practical Engineering

A comprehensive guide to understanding Georg Ohm's fundamental electrical law, the Ohm's law circle formula wheel, limitations, and practical circuit examples.

Key Formulas: V = I × R | I = V / R | R = V / I

Introduction to Ohm's Law

Discovered by German physicist Georg Simon Ohm in 1827, Ohm's Law is the foundational principle of electrical engineering. It describes how potential difference (Voltage), charge flow rate (Current), and material opposition (Resistance) are interrelated in a conducting medium.

The Ohm's Law Formula Wheel

The classic Ohm's Law circle contains 12 standard mathematical formulas connecting Voltage ( $V$ ), Current ( $I$ ), Resistance ( $R$ ), and Power ( $P$ ):

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Solving for Voltage ( $V$ ):

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V = I \times R

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V = \frac{P}{I}

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V = \sqrt{P \times R}

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Solving for Current ( $I$ ):

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I = \frac{V}{R}

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I = \frac{P}{V}

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I = \sqrt{\frac{P}{R}}

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Solving for Resistance ( $R$ ):

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R = \frac{V}{I}

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R = \frac{V^2}{P}

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R = \frac{P}{I^2}

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Solving for Power ( $P$ ):

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P = V \times I

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P = I^2 \times R

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P = \frac{V^2}{R}

Ohmic vs. Non-Ohmic Materials

Ohm's Law applies strictly to ohmic conductors—materials (like standard copper and aluminum wire or carbon resistors) where resistance remains constant regardless of applied voltage. Non-ohmic devices (such as silicon diodes, LEDs, transistors, incandescent lamp filaments, and varistors) exhibit non-linear voltage-current curves and do not follow constant resistance relationships.

Frequently Asked Questions

Does Ohm's Law apply to human skin?

Human skin is largely non-ohmic. Its resistance decreases sharply as applied voltage rises (due to dielectric breakdown of the outer stratum corneum layer) and varies dramatically with moisture and skin contact area.

Related Calculators & Engineering Tools

Ohm's Law Calculator

Resistance Calculator