Alternating Current vs. Direct Current: Lesson for Kids

Instructor: Lori Houston

Lori has a master's degree in creative writing and has taught all subjects at the 5th grade level as well as tutoring 1st- 5th grade students in all subjects

Want to learn more about the electrical power used by all those devices, like televisions and computers and cellphones? In this lesson, you will explore the differences between alternating current and direct current.

How Electrons Flow

Electricity is the flow of electrons through a wire, but there are actually two different ways the electrons move within the wire. These are called currents. Much like an ocean current that moves in a definite direction, electricity has specific movements it makes in the wires. These currents are called alternating current (AC) and direct current (DC).

Direct Current

With DC current, electrons move in one direction, from (-) negative to (+) positive. It's a constant current, flowing continuously until either it's switched off or its power source runs out of or stops generating power.

DC current flow through a simple circuit.
DC current circuit

Let's say we're looking at a circuit with a light bulb. As noted, direct current flows from negative to positive, and the on/off switch acts as a gate for this electron flow. When it's on the circuit is complete, allowing the electrons to flow. After passing through the switch, electrons flow to the light bulb. The filament in the bulb lights up, taking the charge from the electrons, which are then drawn to the positive terminal on the battery to be charged once again. This process continues until the battery eventually loses its charge.

Alternating Current

With AC current, electrons don't really flow, they simply vibrate back and forth from negative to positive and positive to negative. It isn't a continuous vibration either, like the constant flow in DC. The electrons vibrate in time or in sync with one another, and this timing is controlled by modifying the speed of the generator. We call this electrical timing hertz.

In the U.S., AC electricity is generated at 60 hertz. The electrons vibrate and bang into each other, transferring their charge from positive to negative and back again 60 times per second. This means that when a circuit running on AC has a light bulb, it doesn't have a steady flow of positively charged electrons running through it like it does on DC power, so the light is not constant either. It flickers on and off for every cycle of electron charge transfer, at 60 complete cycles per second. However, this is too fast for the human eye to see, so it appears to be a constant light.

AC current flow through a simple circuit.
AC current circuit

AC is produced by a generator, and its charge (negative or positive), flows both ways, as represented by the blue and red arrows in this image. The switch and the bulb operate the same as in the DC circuit.

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