Basic Electrical

Teach Yourself Electricity and Electronics

This book is for people who want to learn basic electricity, electronics, and communications concepts without taking a formal course. It can also serve as a classroom text. This third edition contains new material covering acoustics, audio, high-fidelity, robotics, and artificial intelligence.

I recommend you start at the beginning of this book and go straight through. There are hundreds of quiz and test questions to fortify your knowledge and help you check your progress as you work your way along.

There is a short multiple-choice quiz at the end of every chapter. You may (and should) refer to the chapter texts when taking these quizzes. When you think you’re ready, take the quiz, write down your answers, and then give your list of answers to a friend. Have the friend tell you your score, but not which questions you got wrong.

The answers are listed in the back of the book. Stick with a chapter until you get most of the answers correct. Because you’re allowed to look at the text during quizzes, the questions are written so that you really have to think before you write down an answer. Some are rather difficult, but there are no trick questions.

What you learn?

This book is divided into four major sections:

Direct Current
Alternating Current
Basic Electronics,
Advanced Electronics and Related Technology.

At the end of each section is a multiple-choice test. Take these tests when you’re done with the respective sections and have taken all the chapter quizzes. Don’t look back at the text when taking these tests. A satisfactory score is 37 answers correct. Again, answers are in the back of the book.

There is a final exam at the end of the book. The questions are practical, mostly non mathematical, and somewhat easier than those in the quizzes. The final exam contains questions drawn from all the chapters. Take this exam when you have finished all four sections, all four section tests, and all of the chapter quizzes. A satisfactory score is at least 75 percent correct answers.

With the section tests and final exam, as with the quizzes, have a friend tell you your score without letting you know which questions you missed. That way, you will not subconsciously memorize the answers. You might want to take a test two or three times. When you have gotten a score that makes you happy, you can check to see where your knowledge is strong and where it can use some bolstering.

It is not necessary to have a mathematical or scientific background to use this do-it-yourself course. Junior-high-school algebra, geometry, and physical science will suffice. I’ve tried to gradually introduce standard symbols and notations so it will be evident what they mean as you go. By the time you get near the end of this book, assuming you’ve followed it all along, you should be familiar with most of the symbols used in schematic diagrams.

I recommend that you complete one chapter a week. An hour daily ought to be more than enough time for this. That way, in less than nine months, you’ll complete the course. You can then use this book, with its comprehensive index, as a permanent reference.

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3 Methods of Magnetizing a Steel Bar

In this article, you will learn three principle methods of magnetizing a steel bar.

If a piece of iron or steel is brought near either of the poles of a magnet, it is attracted. If a north pole of a magnet is brought near the south pole of another freely suspended magnet, there is again an attraction between them.

But if two south poles are brought near each other, they repel. The same happens in the case of two north poles. This means that (i) like poles repel each other and (ii) unlike poles attract each other.

From the above, it is clear that a magnet attracts pieces of iron or steel but repels only magnets. Therefore repulsion is a sure test of magnetism.

Now let’s understand how a can we magnetize a steel bar.

Methods of Magnetization

There are three principal methods of magnetizing a steel bar as given below:

Touch method
by means of electric current
Induction method.

1. Touch Method

This method can be further divided as

Single touch method
double touch method
divided touch method.

(a) Single Touch Method

In the single touch method, the steel bar to be magnetized is rubbed with either of the poles of a magnet, keeping the other pole away from it.

single touch method of magnetization — Single touch method

Rubbing is only done in one direction as shown. The process should be repeated many times for the magnetization of the bar.

(b) Double Touch Method

In this method, the steel bar to he magnetized is placed over the two opposite pole ends of a magnet and the rubbing magnets are placed together over the center of the bar with a small wooden piece in between, as shown.

double touch method of magnetization — Double touch method

They are never lifted off the surface of the steel bar, but rubbed again and again from end to end, and finally ending at the center where the rubbing was started.

(c) Divided Touch Method

Here the two different poles of rubbing magnets are placed as in the previous case. They are then separated along the surface of the steel bar to the opposite ends.

The rubbing magnets are then lifted off the surface of the steel bar and placed back in the center of the bar. This whole process is repeated again and again as shown.

The steel bar thus magnetized becomes a permanent magnet but the degree of magnetization is very low.

2. By Electric Current

The bar to be magnetized is wound with insulated copper wire and then a strong electric current (dc) from a battery is passed through the wire for some time. The steel bar then becomes highly magnetized.

If the bar is of soft iron, the magnetism remains as long as the current continues but almost completely disappears as soon as the current ceases. The magnet made by such an arrangement is called an electromagnet and is generally used in laboratories.

3. Induction Method

This is a commercial method of making permanent magnets. In this method, a pole charger is used which has a coil of many turns and an iron core inside it as shown below. The direct current supply is fed to the coil through a push-button switch.

The steel piece to be magnetized is placed on the iron core kept inside the coil and the direct current is passed through the coil. The iron core now becomes a powerful magnet and thus the steel piece placed on it also becomes a magnet by induction. The magnetized piece of steel is then lifted up after switching off the current.

Advantages

The following are the advantages of the induction method of magnetization.

In this method, small pieces of steel can easily be magnetized.
It takes very little time to make a magnet.
Steel pieces of any shape can be magnetized easily.

Uses

The induction method is a commercial process for making permanent magnets for speakers, telephones, microphones, earphones, electrical instruments, magnetos, etc.