مفاهيم التيار المتردد الأساسية (Alternating Current Concepts)

The direct current (DC) is similar to a household water supply system; clean water enters through the main supply pipe, distributes to the kitchen and bathrooms, and then wastewater flows through the drainage openings to gather in a single sewage pipe. The water flows here in only one direction: entering from the supply pipe and exiting from the drainage pipe. This is exactly the behavior of direct current (DC), and in the same way, direct electricity flows in circuits.

If you look at a modern wall outlet (in the United States, for example), you will see three contact openings: a long slot, a short slot, and a round hole. In the default case, electricity flows out of the short slot and returns through the long slot; the short slot resembles a faucet, and the long slot resembles a drain.

But this is not the whole story; the electricity supplied through the public power grid is alternating current (AC). This means that the direction of the current flow changes frequently and cyclically:

• During the first half of the time, electricity flows from the short opening to the long opening.
• During the second half of the time, the direction reverses and electricity flows from the long opening to the short opening.

Every trip where the current goes and returns back and forth is called a "full cycle" (Cycle). When the current flows in one direction, it is called a "half cycle" (Half cycle), and when it reverses to flow in the opposite direction, that represents "the other half cycle."

In the illustrated diagrams, the current line is shown as cut on the left side to emphasize that the long slot (connected to the "neutral" wire) remains at a constant value of zero volts (compared to the ground reference). In contrast, the short slot (connected to the "hot" wire) alternates between positive and negative voltage (reviewing the concept of polarity in direct current).

From this standard perspective, the short opening seems to push the current at times and then pull and suck it in at other times, while the neutral wire (the long opening) appears to show no inherent drive for the flow of current.

Here, remember the analogy of "breathing"; where the short opening can be imagined as inhaling electricity and exhaling it up and down. If we apply this analogy to the home water system, we will see that for half the time, water flows from the faucet to the drain, and during the other half, the faucet reverses its action to flush the water back from the drain!

🔄 نموذج البطارية الدوارة (Rotating Battery Model)

One effective way to visualize and understand alternating current is to imagine it through the model of a rotating battery. Picture a regular chemical battery placed on an axis and continuously rotating around itself; for half the time, the battery is oriented in one direction, and for the other half, it flips to take the opposite direction. As a result of this continuous mechanical rotation, the resulting current flowing through the circuit will alternately and periodically reverse its directions.

We always associate the concept of alternating current (AC) with the electricity we get from household wall outlets, but in reality, alternating current exists in many different circuits and components:

• Audio Frequencies (AF): When the pressure of sound waves is converted into electrical pulses by the microphone, the resulting output is an alternating current. The microphone output can vary and fluctuate at a rate starting from 20 times per second and reaching up to 20,000 times per second; this range is called audio frequencies (Audio Frequency AC - AF).
• Radio Frequencies (RF): Radio and communication circuits also operate on alternating current; the key difference here is that the current reverses its direction of flow hundreds of thousands of times per second, and it can reach several billion times per second; these systems are called radio frequency circuits (Radio Frequency - RF).

In the upcoming pages, we will primarily focus on the study and analysis of the alternating current coming from the public power grid; however, the fundamental laws and rules governing alternating current apply with absolute precision to all frequencies without exception.