Voltage (measured in volts, V) is the electrical potential difference between two points in a circuit. It is the "pressure" that pushes electric current through a conductor.
Ohm's Law
Voltage is related to current and resistance by Ohm's Law: V = I × R, where V = voltage (volts), I = current (amps), and R = resistance (ohms). If you know any two values, you can calculate the third.
Common Voltage Standards
- 1.5V: AA/AAA batteries
- 5V: USB charging
- 12V: Car electrical systems, LED strips
- 120V: U.S. household outlets
- 240V: U.S. dryers, ovens, EV chargers; European household standard
Real-World Example
A 60-watt light bulb on a 120V circuit. Using P = V × I: Current = 60 ÷ 120 = 0.5 amps. Using Ohm's Law: Resistance = 120 ÷ 0.5 = 240 ohms. The same bulb on 240V European power would draw only 0.25 amps.
Frequently Asked Questions
What is the difference between AC and DC voltage?
AC (alternating current) voltage reverses direction periodically — this is what comes from wall outlets (120V AC in the U.S.). DC (direct current) flows in one direction — this is what batteries provide. Electronic devices convert AC to DC internally.
Is higher voltage dangerous?
Voltage itself does not kill — current (amps) does. However, higher voltage can push more current through the body. Generally, voltages below 50V are considered safe. Household 120V can be lethal under certain conditions (wet hands, path through the heart).
Why do some countries use 220-240V?
Higher voltage transmits power more efficiently with less current, allowing thinner wires. The U.S. adopted 120V early for safety; most of the world later standardized on 220-240V. U.S. homes actually have 240V available for large appliances.