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Manish Kumar. Xavier Carrasco. Suhasis Mondal. Chimmy Shim. Abhijan Carter Biswas. Edu Daryl Maceren. Dildeep Pallipad. Quick navigation Home. It is time to use the international abbreviations in the equations. This bizarre abbreviation has to do with history, where current used to represented in the French language. Just remember one, and you can work out the rest when needed. The unit of resistance is named after him. Let us imagine that you have attached electrocardiogram ECG leads to your patient.
You then plug the ECG lead plug to its socket in the monitor. Unfortunately, as you are doing this, a piece of dirt gets into the plug. This makes the yellow wire have a poor contact with its counter part, increasing its resistance.
According to Ohms Law, the high resistance affects the voltage and current in the wire, disturbing the ECG tracing. The plug is unplugged and the dirt removed. Now the contact is good and the resistance is now low. The electrons i. The direction of the current will change if the negative and positive poles of the source are exchanged.
Let me try and make things clearer for you. To make the diagrams a little less crowded, I have simplifying them a bit. The potential difference source is represented with a minus and plus sign. The green arrow will show the direction of current. Remember, current always flows from negative to positive. I will now describe to you the difference between DC and AC.
Let us start with DC. Below is a series of images showing a circuit with a DC power source. The repeated images show you what happens over a time period.
You will notice that over time, that the current has NOT changed direction green arrow remains in the same direction. This is the fundamental property of DC: the current does not change direction.
AC is quite weird when compared to DC current. In AC, the negative pole and positive pole of the source exchange themselves repeatedly. Since current travels from negative to positive, this means that the current also changes direction repeatedly.
The series of images below show AC over time. The positive pole and negative pole keep alternating. In response to this, the direction of current also keeps changing repeatedly. This repeated alternating of current direction happens quite fast. In many countries , it happens 50 or 60 times a second i. The animation below may help you to appreciate how rapid this is.
The negative and positive poles alternate 50 times second. If you suffer from photosensitive epilepsy, please skip this animation. You may wonder why someone would produce a weird current in the form of AC.
There are good engineering reasons why we have AC, and this will be discussed later on. For now, we will continue our discussion about the way AC behaves.
An oscilloscope has a screen that shows voltage changes over a time. The vertical axis represents voltage and the horizontal axis represents time. This helps us to visualise how current behaves over time, and will be very useful when we continue our discussion on AC and DC. It measures the potential difference of the heart over time.
Looks familiar? Below is a simplified oscilloscope. Right now, nothing is connected to the oscilloscope probes black and red probes and therefore the the tracing blue line remains on the baseline. Let us connect the oscilloscope to a DC source. The oscilloscope shows a straight line reading blue line above the baseline broken line.
Oscilloscopes show change in direction of current flow by the trace crossing the baseline. Let us reverse the plus and minus poles of the source i. You will see that the trace crosses the baseline from the top to the bottom. Let us change the polarity again, so it is back to how it was before.
Again you will that the oscilloscope shows this change by making the tracing cross the baseline, in this case from the bottom to the top. We first connect it to a DC source such as a battery. You will get a steady tracing above the baseline. Since with DC, the direction of current flow does not change, the tracing does not cross the baseline. Now let us examine AC with the oscilloscope. You know that, unlike DC, the polarity of AC keeps changing, so you would expect to see something like this.
However, the above square waveform is NOT what you see. Instead you will see a waveform that has much more graceful curves, as shown on the oscilloscope on the right below. The reason why you see the graceful curves instead of the sudden square changes is because the polarity in AC does NOT change suddenly as shown below.
The potential first starts to decrease and eventually becomes zero. Then the polarity gets reversed and potential difference starts to rise till it reaches the maximum. The changes in polarity continue in this fashion. This is the waveform that you often see in text books. The above transition will be shown in a step by step manner. As each step is shown, you will see the AC wave form in the oscilloscope.
You would have noticed that AC has periods where there is zero potential difference. During these times the current flow is zero. Normally one does not notice these zero periods because they happen so fast. However, sometimes you can see these off periods in fluorescent lights tube lights. The off periods may make the light flicker faster than what is shown below, the computer animation is not fast enough.
If you look around you will discover that your world is full of symbols. When you are bored have a look around your operating room and you will find plenty of hidden symbols. Typically they will be found on electrical equipment. Look where monitoring leads and power leads connect. The electrical current that comes out of the wall sockets in homes and hospitals is mostly AC.
Let us see how a transformer works. The transformer uses two very important properties in the world of electricity. The first phenomenon used in transformers is that when a wire carries an electric current, it generates a magnetic field. In the example below, the wire coil is carrying direct current DC. The magnetic field is shown as a blue arc. Below, we demonstrate a wire coil carrying alternating current AC. In DC the field is non changing, whereas in AC the field is changing all the time.
Now let us discuss the second electrical phenomenon that makes transformers work. Electromagnetic induction refers to a phenomenon where if a wire or coil of wire as in our example is exposed to a CHANGING magnetic field, a current will be induced in the wire.
In the example below, the changing i. It is important that the magnetic field is changing. A non changing magnetic field as shown below will NOT induce a current in the coil. Now we can explain how the transformer works. The input AC goes into the primary coil pink.
This produces a changing magnetic field blue arc with arrows. The changing magnetic field induces a current in the secondary coil green and in this way, electric energy is transferred from the primary coil to the secondary coil.
At this point you can see that a transformer works only with AC, because it needs a changing magnetic field to transfer energy across it. If you used DC, the transformer would not work. The magnetic field would be non changing and thus would not transfer energy across to the secondary coil. Whether the transformer behaves as a step up or a step down transformer depends on the ratio of the loops in the primary coil and secondary coil. In a step up transformer, the secondary coil has more turns than the primary coil.
Similarly, in a step down transformer, the secondary coil has less turns than the primary coil. Now we understand that transformers can transform the voltage up or down. We also understand that we need AC for transformers to work.
Now the question is, why are transformers so important? It has got to do with the transmission of electricity. Earlier on,we discussed how electricity is generated at the power station. One big headache for the power company is that when electricity travels in wires, it loses energy. If this happens over huge distances, there will be nothing left when the wire reaches you. There is a physics principle that wires carrying a low voltage have higher losses than wires carrying an high voltage.
The explanation for this beyond the scope of this website. These high voltage power lines can often be seen crisscrossing the landscape. Next time you are outside, do have a look for them. This is where transformers come in. Generators produce a relatively low voltage. This low voltage is raised by a step up transformer to an high voltage, which is used to send the electricity over a long distance.
As the wires reach you, the high voltage is reduced using a series of step down transformers. The only practical way to generate the high voltages and subsequent reduction needed for economical power transmission is to use transformers. And that is why AC is used for power transmission, all way to the wall socket in your hospital and home.
It is important that you know about electricity. It will help you to better understand electrical safety. There are many sources of potential difference such as batteries, electrical supply sockets at home and hospital etc. Current is directly related to the potential difference, and this forms part of Ohms Law.
Resistance is something that resists current flow and is measured in Ohms. Current is inversely proportional to resistance. This relationship forms part of Ohms Law. Ohms Law defines the relationship between voltage, current, and resistance.
If you know two of the three components of Ohms Law, you can find out the third. Current can be DC or AC. In DC, the electrons flow in one direction whereas in AC, the electrons alternate their direction.
You know thanks to a oscilloscope how DC and AC behaves over time. You know how the AC waveform is formed. Transformers are needed to make high voltages needed to economically send current over long distances. Transformers work only with AC, and that is why the power company supplies your home and hospital with AC. Learning about basic electronics and creating your own projects is a lot easier than you may think. You will then learn about schematic diagrams and how they are used to design and build circuits.
And finally, you will put this information to use by creating your first basic circuit. Before you get started, make sure your electronic workbench is properly set up. The most popular option is to use clear plastic storage boxes for storing parts. It serves as an excellent reference to unchain the mysteries of electronic circuits.
Sometimes you may find difficulty in choosing the right book for your project. For your convenience, our team of experts have done hours of research and brought you these 15 electronic books to choose from the best, that match your requirements. Also check —. Best Electronic Books Reviews 1. In order to provide our services we rely on a series of essential cookies to access our features. We also use a set of 3rd party cookies that allow us to deliver a better experience. Please read our Privacy Policy page , and if you agree, please click on the button below ot enter the site.
Engineering Mathematics: YouTube Workbook. Introduction to Electronic Engineering. Introduction to Complex Numbers. Essential Engineering Mathematics. Automation and Robotics. Wooah this is the most sought after at the moment, and the good news is that these two books are now available on our service, would you like to read them in full??
But before reading a little synopsis first, I will include it below The text covers all aspects of basic theory principles new learners need to know.
Its clear presentation uses schematics and large illustrations to bring concepts to life, while examples throughout demonstrate how to do common tasks electricians perform. An interactive online course mode called Mindtap that includes the entire text, multi-media assets, customization and social media options will be available. Mais avant de lire d'abord un petit synopsis, je vais l'inclure ci-dessous.
As a child, he dreamed of becoming an electrical engineer. But he soon discovered that he loved writing as much as he loved electronics, and his first technical book was published in Since then, he has written more than. Ammeters are always connected in series with the circuit to be tested. It is obtained by multiplying the current in amperes by the time in hours during which current flows.
For example, a battery which provides 5 amperes for 20 hours is said to deliver ampere - hours. One ampere is equal to a current flow of one coulomb per second.
Apparent power is the product of the rms voltage and the rms current. Electrical Wiring. Download Repair Manual Pdf. Building Electrical Wiring Symbols. Electrical Panel Diagram U Untpikapps. Wiring Diagram Of Building. Thank you for visiting nature. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser or turn off compatibility mode in Internet Explorer.
In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. Learning - Basics of Electricity. In order to understand even the simplest concepts of electronics, you must first understand what electricity is. Author: Cathleen Shamieh, Gordon McComb All books, brand names, logos and trademarks in this site are property of their respective company owners,writers and publishers.
Microwave ovens and hair dryers are 1, or 1, watts. Electric Circuit Analysis by K. Suresh Kumar. We will discuss the following aspects. Please scroll down and start reading.
Why should you understand electricity Current and amperes Potential difference and volts Relationship between potential difference and current Sources of potential difference Concept of resistance Ohms Law DC and AC current According to psychologists, the human mind has a tendency to make certain mistakes when thinking and this can make one think in very nonsensical ways. Why should you know about electricity? Learning a bit about electricity is useful because: It will provide the basics for understanding electrical safety.
It will help you to better understand the principles of electrical medical equipment such as electrosurgical devices, defibrillators, temperature measurement etc. In reality, it is really tough to count zillions of electrons. So in summary, ampere relates to the amount of electrons flowing across a wire per second.
You cannot understand why. Let us see the wire in close up to see why the bulb is not lighting You will see that the electrons in the wire are moving randomly in all directions.
A typical house hold battery has 1. For an example, the symbol for a battery is: The shorter vertical line represents the negative pole. Similarly, a light bulb can be represented by a symbol. Relationship between potential difference and current. Single use batteries : So far in our discussions we have used batteries as our source of potential difference.
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