AI Tutor
A static shock from a doorknob can carry thousands of volts, yet it only stings for a microsecond. Meanwhile, a 120-volt wall outlet can be lethal.
The danger doesn't come from energy aloneβ€”it depends on how much charge flows, how hard it is pushed, and what resists its journey.
To understand how any circuit operates, we first have to measure the moving charges themselves. What controls that flow?

Electric Current: Charges on the Move

Electric current is the rate at which electric charge flows through a cross-section of a conductor.
We represent current with the symbol II and measure it in amperes (often shortened to amps, A\text{A}), where one ampere equals one coulomb of charge passing per second: I=Ξ”QΞ”tI = \frac{\Delta Q}{\Delta t}
In metal wires, the mobile charges are negatively charged electrons that slowly drift through the metal lattice while electrical energy travels along the wire nearly at light speed.
In the 1700s, Benjamin Franklin guessed that positive charges were the ones moving, establishing the rule for conventional current (positive to negative), which scientists still use today even though electrons physically travel toward the positive terminal.
Charges will not move on their own, though. What gives them the push to form a current?

Voltage: The Electrical Push

Voltage, formally called electric potential difference, is the amount of work or electric potential energy given to each unit of charge.
Measured in volts (V\text{V}), one volt equals one joule of energy per coulomb of charge (1Β V=1Β J/C1\text{ V} = 1\text{ J/C}): V=Ξ”PEqV = \frac{\Delta PE}{q}