## Thursday, August 20, 2009

### What is Electric Circuit? - Part 2

Before I proceed with our new topic for today, I just want to give thanks for those who are currently subscribed here in Learn Electrical Engineering for Beginners. I hope this will be a helpful site for you which I will always give a full and detail information for every subject matter.

Well, it's enough for my short introduction because I'm already running out of time for the updates. Yesterday I had mentioned on my previous post about our topic on full definition of Electric Circuits that I will going to differentiate between DC and AC Circuits. Please keep in mind that after discussing the difference between the two, I will going to discuss first to you all DC Circuits related topics so that we would not be confused. The principles that we will be discussing here in DC Circuits will also be used again when we touch AC Circuits. Please keep that in mind and this is very important. I just want to keep my ideas and discussions organize here in Electrical Engineering site. I was also trying to catch up the attention of those Electrical Engineering who study online as well as those non- electrical engineers.

Moving on...

Still remember on our review on Physics on my previous post in Voltage, Current, Power and Energy. I already give the definition of DC and AC Current. But for those recent readers, here is the short definition and which is almost the same when dealing with circuits.

In electricity, we deal both on direct current (DC) and alternating current (AC). In DC Circuits, the current always flows in the same or one direction. In AC Circuits, the direction of current flow reverses periodically- this means at one instant the current flow in one direction and in the next instant, in the opposite direction. Remember in our review? this flow reversal in AC current is usually done regularly. What does it mean? If we talk about 60Hz AC power, we mean that the direction of flow reverses 60 times ( or cycles) per second. Graphically, here are the difference for you to comprehend it well. ( You may click the image to enlarge)

Ohhh... before I forgot there are other types of current such as Exponential Current and Dumped Sinusoidal Current. But these are somewhat on the deeper concepts that we might be able to touch on our future discussion. But to give you an idea here are the graphical difference between the two. ( You may click the image to enlarge)

As what I had mentioned earlier, on the first part of the circuitry discussion we will deal with the function of direct current in circuits containing resistance (resistive circuits) and we will use Ohms Law and Kirchhoff's Laws as the tools for analysis and understanding the relationship between current, voltage and resistance. This will be your foundation for your future understanding of ac circuitry. Therefore, it is very important that you completely understand every concept I presented here in dc circuitry.

Continuing our understanding of Electric Circuit.

It may help you to grasp the concept of an electric current flowing through a closed circuit. Imagine that the electrons which make up the current form a moving stream which revolves through the complete circuit.

This moving streams of electrons maintains a constant density throughout its entire length. The number of electrons entering the positive terminal of a battery from a wire is always exactly balanced by the number of electrons which the battery forces to move its own negative terminal and out into the wire.

Therefore, there is no way either the conductor wire or the battery possess either more or less electrons in a complete circuit. If the circuit loop is broken, the electron orbiting stream instantly stops revolving through the circuit; but both wire and battery will still hold exactly same number of electrons as they did when the circuit was made. The only difference is that the wire is now holding some of the electrons which was previously in the battery. Likewise, the battery had taken an equal number from the wire.

The number of electrons in the electron stream is depends on the strength of the voltage applied forcing the electrons to move. The lower the voltage, the weaker.

I will just tell you this in advance that when a resistance of any kind is inserted into the circuit loop, it also restrict the number of electrons flowing therefore reduces the current. You will notice that in some of our applications when we touch different circuitry laws. The flow of current is restricted by this resistance.

Also keep in mind a closed loop of wire is not always an electric circuit. Remember that in our definition of Electric Circuits, I had mentioned there the 2 conditions that makes up an electric circuit. Current, voltage and resistance are present in any electric circuit where electrons move around the close loop. The pathway for current flow is actually the circuit, and its resistance controls the amount of current flow around the circuit.

DC circuits consists of a source of DC voltage, such as batteries plus the combined resistance of the electrical load connected across this voltage. While working with DC circuits, you will find out how the total loads can be changed with various combinations of resistances, and how these combination of resistances control the circuit current and affect the voltage. This concept will also be applied in AC circuitry.

There will be two types of circuits that we will be dealing with: these are series circuits and parallel circuits. No matter how complex the circuit is, still it can be simplified down into series connection to or a parallel circuit connection.

One last thing.

Previously on our last topic we had mentioned about the load in the electric circuit. So what the heck is the load? How does it works in the electric circuit?

In basic electric circuit the device that transforms the electrical energy from the source of power (emf) into some useful function -such as heat, light, mechanical power, etc.- is called the load. The load aside from transforming and electrical energy into some useful purposes, can be utilized to changed or control the amount of energy being delivered from the source.

A load could be a motor, a telephone, a lamp, a heater or some other appliances -( name it ). the term load means the electric power delivered by the source. If you don't get it, I will give you an example. When it is stated that the load is increased or decreased, it means that the source is delivering less or more power. Remember a load can be: a device which utilizes the power from the source and the power that is taken from the source.

One more last thing...

The Switches

I included this because this is one of the common part of electric circuitry either on DC or AC Circuitry. We have been using switches everyday and all our life. We could see it in our lamps, a radios, flahlights etc. It is a controlling device which open and close the circuit. There are many types of switches you will encounter in your study of Electrical Engineering. But this will be discussing separately when we touch practical applications in our course outline.

This is where it ends our topic discussing what an electric circuit is. On my succeeding post, we will now begin to study in detail the relationship between voltage, current and resistance.

Hope you appreciate this post today presenting it in my own little way. Learning is fun here in Electrical Engineering for Beginners.

Cheers!