Ohm's Law Power Wheel
The complete Ohm's law power wheel with all 12 formulas relating voltage, current, resistance, and power in electrical circuits.
The Core Formulas
Ohm's law (V = IR) and the power equation (P = IV) can be combined to produce 12 formulas. The "power wheel" organizes all of them so you can find any quantity from any two known quantities.
Variables
| Symbol | Meaning | Unit |
|---|---|---|
| V | Voltage (potential difference) | Volts (V) |
| I | Current (flow of charge) | Amperes (A) |
| R | Resistance (opposition to current) | Ohms (Ω) |
| P | Power (rate of energy transfer) | Watts (W) |
All 12 Formulas
Find Voltage (V)
Find Current (I)
Find Resistance (R)
Find Power (P)
How the Wheel Works
Given any two of the four quantities (V, I, R, P), you can calculate the other two. Choose the formula that contains your two known values and the unknown you want to find.
Example 1
A 12V car battery powers a headlight that draws 5 Amps. What is the resistance and power?
Resistance: R = V/I = 12/5 = 2.4 Ω
Power: P = IV = 5 × 12 = 60 W
R = 2.4 Ω, P = 60 Watts
Example 2
A 100W light bulb operates at 120V. What current does it draw, and what is its resistance?
Current: I = P/V = 100/120 = 0.833 A
Resistance: R = V²/P = 120²/100 = 14,400/100 = 144 Ω
I = 0.833 A, R = 144 Ω
Example 3
A resistor dissipates 2 Watts and has a resistance of 50 Ω. What is the voltage across it?
Voltage: V = √(PR) = √(2 × 50) = √100
V = 10 Volts
When to Use It
The Ohm's law power wheel is the most fundamental tool in electrical engineering and electronics.
- Designing and analyzing electrical circuits
- Sizing wires, fuses, and circuit breakers
- Calculating electricity costs (power × time = energy used)
- Selecting resistors and other components
- Troubleshooting electrical problems by measuring and comparing values
- Understanding home electrical systems, batteries, and appliances