Ohm's Law Calculator
Free calculate voltage, current, or resistance using v = ir. solve for any variable. Get instant, accurate results with our easy-to-use calculator.
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What is Ohm's Law?
Ohm's Law is a fundamental relationship in electrical engineering that describes how voltage, current, and resistance are related in a circuit. It states that voltage equals current times resistance: V = I × R.
Named after German physicist Georg Simon Ohm, this law applies to linear resistive circuits. It's one of the most important principles in electronics and electrical engineering, forming the basis for circuit analysis.
Ohm's Law allows you to calculate any one of the three quantities (voltage, current, resistance) if you know the other two. It's essential for designing circuits, troubleshooting electrical problems, and understanding how electrical systems work.
Ohm's Law Formula
Where:
- • V = Voltage (V)
- • I = Current (A)
- • R = Resistance (Ω)
Rearranged:
I = V / R
R = V / I
How to Calculate
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1
Identify what to solve for
Determine whether you need voltage, current, or resistance.
-
2
Convert to SI units
Convert mA to A, kΩ to Ω for consistent calculations.
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3
Apply the formula
Use V = I×R, I = V/R, or R = V/I as appropriate.
Practical Examples
Example 1: Calculate Voltage
A 10 Ω resistor carries 2 A of current. What is the voltage?
Solution:
V = I × R = 2 A × 10 Ω
V = 20 V
Example 2: Calculate Current
A 12 V battery is connected to a 6 Ω resistor. What current flows?
Solution:
I = V / R = 12 V / 6 Ω
I = 2 A
Example 3: Calculate Resistance
A 24 V source produces 3 A of current. What is the resistance?
Solution:
R = V / I = 24 V / 3 A
R = 8 Ω
Applications
Circuit Design
Calculating component values, voltage drops, current requirements, and designing electrical circuits.
Troubleshooting
Diagnosing electrical problems, measuring circuit parameters, and verifying expected values.
Power Systems
Understanding voltage regulation, current limits, and resistance in power distribution systems.
Education
Teaching fundamental electrical principles and circuit analysis in physics and engineering courses.
Frequently Asked Questions
Does Ohm's Law apply to all circuits?
Ohm's Law applies to linear resistive circuits. It doesn't apply to non-linear components (diodes, transistors) or AC circuits with reactive components (inductors, capacitors) without modification.
What is the power relationship?
Power can be calculated from Ohm's Law: P = V×I = I²R = V²/R. These are derived by combining Ohm's Law with the power formula.
Why is resistance measured in ohms?
The ohm (Ω) is the SI unit of resistance, named after Georg Ohm. 1 Ω = 1 V/A, meaning 1 volt per ampere of current.
What happens if resistance is zero?
If R = 0 (short circuit), current becomes infinite (or very large) for any voltage. This is why short circuits are dangerous - they can cause fires and damage equipment.
What happens if resistance is infinite?
If R = ∞ (open circuit), current becomes zero regardless of voltage. This is an open circuit - no current flows, but voltage can still be present.