Ohm's Law
Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across those points, provided temperature and other physical conditions remain constant. It is one of the most fundamental relationships in electrical engineering and circuit analysis. The law applies to ohmic (linear) materials and is used to calculate unknown voltages, currents, or resistances in simple circuits.
Key Formula
V = I × R
LaTeX: V = I \times R
| Symbol | Meaning | Unit |
|---|---|---|
| V | Voltage (potential difference) | Volt (V) |
| I | Electric current | Ampere (A) |
| R | Electrical resistance | Ohm (Ω) |
Worked Example
Problem
A resistor has a resistance of 47 Ω. A current of 0.2 A flows through it. Find the voltage across the resistor.
Solution
Step 1: Identify values: R = 47 Ω, I = 0.2 A. Step 2: Apply Ohm's Law: V = I × R = 0.2 × 47 = 9.4 V.
Answer
V = 9.4 V
Ohm's Law Rearrangements and Their Uses
| Find | Formula | Known Values | Example |
|---|---|---|---|
| Voltage (V) | V = I × R | Current and resistance | V = 2 A × 5 Ω = 10 V |
| Current (I) | I = V / R | Voltage and resistance | I = 12 V / 4 Ω = 3 A |
| Resistance (R) | R = V / I | Voltage and current | R = 9 V / 3 A = 3 Ω |
| Power (P) | P = V²/ R = I²R | Any two of V, I, R | P = 4² / 2 = 8 W |
Interactive Tools
Wikimedia Commons, CC BY-SA
Related Terms
Electric Current
Electric current is the rate of flow of electric charge through a conductor, measured as the amount of charge passing a cross-section per unit time. It is the fundamental quantity that drives electrical circuits and powers all electronic devices. In metallic conductors, current arises from the drift of free electrons, while in electrolytes and plasma it involves the movement of ions.
Electrical Resistance
Electrical resistance is the opposition that a material offers to the flow of electric current, quantifying how much a conductor restricts charge flow for a given applied voltage. It depends on the material's resistivity, its length, and its cross-sectional area, and increases with temperature in most metals. Resistance is central to controlling current in circuits and forms the basis of Ohm's Law.
Electrical Power
Electrical power is the rate at which electrical energy is transferred or consumed by a device, equal to the product of the voltage across it and the current through it. It determines how quickly a device does work or dissipates energy as heat, light, or motion. Power is critical in the design of electrical systems, from household appliances rated in watts to large industrial generators rated in megawatts.
Named after German physicist Georg Simon Ohm who published his findings in "Die galvanische Kette, mathematisch bearbeitet" (1827). The term "Ohm's Law" was coined by subsequent scientists honouring his empirical discovery of the proportional relationship between voltage and current.