Voltage, Current & Resistance

The Big Three

Voltage, current, and resistance are the three fundamental quantities in electrical circuits. Understanding the relationship between them is the foundation of all electronics.

Voltage (V)

Voltage is the electrical pressure that pushes electrons through a conductor. It's the difference in electric potential energy between two points in a circuit. Voltage is measured in Volts (V), named after Alessandro Volta who invented the first battery.

Current (I)

Current is the rate of flow of electric charge through a conductor. It measures how many electrons pass a given point per second. Current is measured in Amperes (A), often shortened to Amps. The symbol 'I' comes from the French 'intensité du courant' (intensity of current).

Resistance (R)

Resistance is a material's opposition to the flow of current. Every material has some resistance — conductors have very low resistance, while insulators have very high resistance. Resistance is measured in Ohms (Ω), named after Georg Simon Ohm.

Resistance depends on four factors: the material (resistivity), length of the conductor, cross-sectional area, and temperature. Longer wires have more resistance; thicker wires have less.

The Water Analogy

• •Voltage = Water pressure (how hard the water is being pushed)
• •Current = Flow rate (how much water flows per second)
• •Resistance = Pipe restriction (a narrow pipe resists water flow, just as resistance opposes current)