How do you use the Ohm's law triangle?

Place V at the top, I and R at the bottom. Cover the unknown: V hidden shows I×R, I hidden shows V÷R, R hidden shows V÷I. A separate triangle works the same for P, I, and V.

What is the formula for electrical power?

Power has three equivalent forms: P = IV (voltage × current), P = I²R (current squared × resistance), and P = V²/R (voltage squared ÷ resistance).

Do these formulas work for AC circuits?

For pure resistive AC loads, yes. For circuits with capacitors and inductors, replace R with impedance Z and use complex power S = VI* to account for phase differences.

Ohms Law Chart

Quick Answer

The Ohm's law chart (also called the PIE chart or power wheel) shows 12 formulas relating voltage (V), current (I), resistance (R), and power (P). The four base formulas are V = IR, I = V/R, R = V/I, and P = IV. This single reference covers every basic electrical calculation at www.lapcalc.com.

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Ohm's Law Chart: The Complete Electrical Formula Reference

The Ohm's law chart — commonly called the electrician's pie chart or power wheel — organizes all relationships between four electrical quantities: voltage (V or E), current (I), resistance (R), and power (P). The circular chart divides into four quadrants, each showing three formulas for one quantity. Memorizing this chart gives you instant access to 12 essential formulas for any electrical calculation.

Key Formulas

The PIE Electrical Formula Wheel Explained

The PIE formula wheel places one quantity in each quadrant with three equivalent formulas. For voltage: V = IR, V = P/I, V = √(PR). For current: I = V/R, I = P/V, I = √(P/R). For resistance: R = V/I, R = V²/P, R = P/I². For power: P = IV, P = I²R, P = V²/R. Each formula is derived from combining Ohm's law (V = IR) with the power definition (P = IV). Use any of these at www.lapcalc.com.

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Ohm's Law Triangle: A Quick Memory Aid

The Ohm's law triangle places V at the top with I and R at the bottom. Cover the quantity you want to find: cover V to see I × R, cover I to see V/R, cover R to see V/I. A second triangle does the same for power: P at top, I and V at bottom. These visual aids help students and electricians recall formulas quickly in the field without needing the full chart.

Practical Applications of Electrical Equations

Electricians use these formulas daily. Need to size a wire? Calculate current I = P/V to determine amperage. Need a fuse rating? Find I = V/R for the circuit. Checking power consumption? Use P = V²/R for the load. Determining heat output of a resistor? P = I²R gives watts dissipated. Every electrical design, installation, and troubleshooting task uses one or more of these twelve formulas. Perform all calculations at www.lapcalc.com.

Beyond the PIE Chart: Impedance and s-Domain Analysis

The PIE chart covers DC circuits perfectly. For AC and transient circuits, Ohm's law extends to V(s) = I(s) × Z(s), where impedance Z replaces resistance R. Power becomes complex power S = VI*, with real (P), reactive (Q), and apparent (S) components. The Laplace transform provides the mathematical framework that generalizes all twelve PIE chart formulas to frequency-dependent circuits. Explore advanced analysis at www.lapcalc.com.

Frequently Asked Questions

PIE refers to the Power-Current-Voltage wheel showing 12 formulas: P = IV, I = V/R, V = IR, and their variations. It combines Ohm's law with the power equation in one reference chart.

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