A flashlight bulb and a desk lamp both glow. Inside their wires, the two currents are doing different things.
Back in the Circuits topic, you saw that an electric current is a flow of charge. The difference here is the direction of that flow.
In the flashlight, the battery drives the charge around the loop in one direction, all the time.
Current that always flows one way is called direct current, or DC. A battery supplies DC.
The desk lamp plugs into a wall outlet. In its wires, the current flows one way, then the other, swapping back and forth many times each second.
Current that repeatedly reverses direction is called alternating current, or AC. A wall outlet supplies AC.
A car battery also drives the charge one way, all the time. A car battery supplies DC.
A toaster plugs into a wall outlet too, so its current repeatedly reverses. The toaster runs on AC.
A smoke detector runs on a 9 V battery. Which kind of current flows in it?
A battery drives the charge one way, all the time.
Current that always flows one way is direct current.
Direct current (DC) flows in the smoke detector.
A TV remote runs on two batteries. Which kind of current flows in it?
In a wire, the current flows one way, then the opposite way, 60 times each second. Which kind of current is it?
The current repeatedly reverses its direction.
Current that repeatedly reverses direction is alternating current.
It is alternating current (AC).
In a lab wire, the current reverses direction ten times each second. Which kind is it?
Which kind of current repeatedly reverses its direction?
Which pairing of supply and current kind is correct?
Four currents are measured. In wire J, the current flows one way, steadily. In wire K, it reverses direction 60 times each second. In wire L, it flows one way, slowly getting weaker. In wire M, it flows one way, in short pulses. Which wire carries alternating current?
A phone charger's label reads 'output: DC'. What does the label say about the current the charger gives out?