Is V = I R always true?

It is an excellent model for ohmic materials in many practical regimes. Semiconductors, vacuum tubes, superconductors, and circuits with reactive components need richer descriptions; even resistors depart from strict linearity at high temperature or high frequency.

Which forms of power follow from Ohm's law?

Electrical power delivered to a resistor can be written P = V I, and substituting Ohm's law gives P = I²R or P = V²/R. Each form is convenient depending on whether you hold current or voltage fixed in a thought experiment.

How does this relate to series and parallel resistors?

Ohm's law applies to each branch individually. Equivalent resistance formulas combine branches so that the same V–I relation holds for the network as seen by the source, which is how the simulator's larger circuit pages stay consistent with this page.

Why might a real meter disagree slightly with the ideal V = I R readout?

Meters have internal resistance, thermal drift, and digitization noise. The ideal relation assumes a pure lumped resistor and perfect measurement taps.

Ohm's Law

Adjust voltage and resistance. See current change with interactive V-I graph.

Live graphs

About this model

Ohm's law states that for many conductors under ordinary conditions, voltage V, current I, and resistance R satisfy V = I R. Microscopically it reflects a balance between the electric driving field and scattering for charge carriers; macroscopically it is the constitutive relation used to analyze resistor networks, power dissipation P = I²R = V²/R, and operating points of simple circuits. The simulator highlights how changing one quantity constrains the others when R is fixed, and when it is pedagogically useful to treat R as a slider to explore non-static intuition (e.g., temperature-dependent resistance is not modeled explicitly here). Idealizations include lumped, linear resistors, steady DC or slowly varying quasi-static currents, and negligible parasitic inductance or capacitance. Students should connect this law to Kirchhoff's rules: Ohm's law assigns branch currents given voltages, while KCL and KVL enforce conservation across the topology.

Who it's for: Beginners in electricity and electronics learning to read schematics, compute power, and relate measurements on meters to algebraic circuit models.

Key terms

Ohm's law
Voltage
Current
Resistance
Conductance
Electrical power
Linear resistor
DC circuit

How it works

Ohm's law: for many metallic conductors at constant temperature, current through a resistor is proportional to the voltage across it, I = V/R. The V–I curve is a straight line through the origin; its slope is the conductance 1/R.

Key equations

I = V / R

P = V I = V² / R = I² R

Frequently asked questions

Is V = I R always true?: It is an excellent model for ohmic materials in many practical regimes. Semiconductors, vacuum tubes, superconductors, and circuits with reactive components need richer descriptions; even resistors depart from strict linearity at high temperature or high frequency.
Which forms of power follow from Ohm's law?: Electrical power delivered to a resistor can be written P = V I, and substituting Ohm's law gives P = I²R or P = V²/R. Each form is convenient depending on whether you hold current or voltage fixed in a thought experiment.
How does this relate to series and parallel resistors?: Ohm's law applies to each branch individually. Equivalent resistance formulas combine branches so that the same V–I relation holds for the network as seen by the source, which is how the simulator's larger circuit pages stay consistent with this page.
Why might a real meter disagree slightly with the ideal V = I R readout?: Meters have internal resistance, thermal drift, and digitization noise. The ideal relation assumes a pure lumped resistor and perfect measurement taps.

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Frequently asked questions

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Key equations

Frequently asked questions