Slide 1
Voltage measures energy per charge; current measures charge per time
Voltage measures energy difference per unit charge. Current measures how much charge passes a point per unit time.
More to Read
A circuit can have a voltage across an open switch while carrying essentially no steady current through it. The two quantities describe different aspects of a circuit, so one cannot substitute for the other.
Slide 2
A component transfers energy without consuming charge
In a steady simple circuit, charge entering a component also leaves it. The component transfers energy rather than using up the current.
More to Read
Electrons already exist throughout a metal wire. A lamp begins responding as the electromagnetic signal establishes around the circuit, not after one electron has completed the entire journey from the power source.
Slide 3
An ohmic component links current, voltage and resistance
For an ohmic component at fixed conditions, current equals voltage divided by resistance. This relation describes a component’s response.
More to Read
Real components need not have constant resistance. A filament heats as current increases, changing its resistance; a diode has a strongly nonlinear current–voltage relationship, so a single fixed ratio is insufficient.
Slide 4
Direct-current power multiplies voltage by current
For a direct-current component, electrical power equals voltage across it multiplied by current through it. Both measurements are needed.
More to Read
A component with 5 volts across it and 2 amperes through it transfers 10 watts. Whether that becomes useful motion, light or heat depends on the component and the task.
Slide 5
Voltage is measured between points; current through a path
Voltage is measured between two points. Current is measured through a path, so the instruments interact with circuits in different ways.
More to Read
An ideal voltmeter draws negligible current, while an ideal ammeter adds negligible resistance in series. Real instruments depart from those ideals and can alter the circuit being measured, especially in sensitive experiments.
Sources
- Basics of Electricity, Energy
National Renewable Energy Laboratory
- Energy Basics
US Department of Energy / NREL