Electronics

A First Course

Owen Bishop

• Publisher: Routledge
• Year: 2010
• eBook ISBN: 9781136440359
• Edition: 3
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

Owen Bishop's First Course starts with the basics of electricity and component types, introducing students to practical work almost straight away. No prior knowledge of electronics is required. The approach is student-centred with self-test features to check understanding, including numerous activities suitable for practicals, homework and other assignments. Multiple choice questions are incorporated throughout the text in order to aid student learning. Key facts, formulae and definitions are highlighted to aid revision, and theory is backed up by numerous examples within the book. Each chapter ends with a set of problems that includes exam-style questions, for which numerical answers are provided at the end of the book. This text is ideal for a wide range of introductory courses in electronics, technology, physics and engineering. The coverage has been carefully matched to the latest UK syllabuses including GCSE Electronics, GCSE Design & Technology, Engineering GCSE and Edexcel's BTEC First in Engineering, resulting in a text that meets the needs of students on all Level 2 electronics units and courses. Owen Bishop's talent for introducing the world of electronics has long been a proven fact with his textbooks, professional introductions and popular circuit construction guides being chosen by thousands of students, lecturers and electronics enthusiasts.

Part 1

Electricity

Topic 1

Electrons

Put some small pieces of kitchen foil on the workbench. You can use small pieces of cork, instead. Rub a plastic pen with a dry woollen cloth. Rub hard for ten or twenty seconds. Hold the pen a few millimetres above the pieces of foil. They jump up and stick to the pen. Some of them may jump up and down again several times.

Figure 1.1

Figure 1.2

The reason that the pieces jump is that they are attracted by electrons on the pen. Rubbing the cloth on the pen has made electrons from the cloth transfer to the pen. We say that the pen is charged with electrons. It has an electric charge.

Some other things can be charged by rubbing. Rub a balloon with a cloth (or against your clothes). Then place it in contact with the wall of the room. It does not fall down to the floor but stays where you put it, on the wall. The electric charge has produced an electric force that holds the balloon against the wall.

Figure 1.3

Things to do

You need two strips of polythene, about 30 cm by 2 cm, and a soft dry cloth. Put the strips on the workbench and rub them briskly with the cloth. Pick up the strips by one end, one in each hand. Hold them about 50 cm apart. Then slowly move them together.

Repeat this, using one strip of polythene and one strip of acetate sheet. What do the strips do now?

Figure 1.4

Self Test

What do you expect will happen if you try to bring two charged acetate strips together?

KINDS OF CHARGE

You have found that:

• Two charged polythene strips repel each other. They try to stay apart.

• A polythene strip and an acetate strip attract each other. They try to come together.

It seems that the charge on acetate is different from that on polythene, so:

There are two kinds of charge

Two charged polythene strips repel each other, so:

Like charges repel

Two differently charged strips attract each other, so:

Unlike charges attract

Self Test

Pieces of foil jump up to a charged plastic pen. Then some of them jump down again. Why does this happen?

POSITIVE AND NEGATIVE CHARGE

The two kinds of charge are called positive charge and negative charge. These names do not mean that positive charge has something that negative charge does not have. They just mean that the charges are of opposite kinds.

Rubbing a polythene strip with a cloth transfers some of the electrons from the atoms in the cloth on to the strip. Electrons have negative charge, so the strip becomes negatively charged. Also, the atoms of the cloth have now lost some electrons. This makes the cloth positively charged.

Rubbing an acetate strip with a cloth does the opposite. It removes electrons from the strip, leaving it positively charged. The cloth gains electrons and becomes negatively charged.

USING ENERGY

Positive and negative charges always attract each other. They try to come together. When you rub the cloth on the plastic, you separate the negative charge from the positive. It takes energy to pull them apart when they are trying to come together. This energy comes from the muscles of your arm.

ELECTRONS

Electrons are too small to see, even with a powerful microscope.

Electrons are too light to weigh. You need 1 000 000 000 000 000 000 000 000 000 000 electrons to weigh 1 kg (an amazing fact that you do not need to remember).

Figure 1.5

The most important fact about electrons is that they carry negative electric charge. The charge on a single electron is extremely small. But, if you have enough of them (as on the pen or the charged polythene), you can show the force that their charge causes. There are lots more things that we can do with electrons, as you will find out as you work through the book.

Self Test

Why is it impossible to have a pile of electrons, like that shown in the drawing?

ELECTRONS AND ATOMS

Matter is made up of molecules of many different kinds. Molecules are made up of one or more atoms. Atoms are made up of electrons (negatively charged), protons (positively charged) and neutrons (uncharged).

The simplest possible atom consists of one electron and one proton. The proton is at the centre of the atom and the electron is circling around it, in orbit.

Figure 1.6

With one unit of negative charge on the electron and one unit of opposite but equal charge on the proton, the atom as a whole is uncharged.

The electron is circling at high speed around the proton, like a planet orbiting the Sun. There must be a force to keep it in orbit. In the case of a planet the force is gravity, the attraction between the masses of the Sun and the planet. In the case of the electron the force is the electrical attraction between oppositely charged bodies. The experiments on pages 3–4 demonstrated this.

OTHER KINDS OF ATOM

There are more than a hundred different elements in nature, including hydrogen, helium, copper, zinc, iron, mercury and oxygen, to name only a few.

Each element has its own distinctive structure, the atoms being made up of fixed numbers of electrons and protons.

In spite of these differences, all elements have the same basic plan. There is a central part, called the nucleus, where most of the mass of the atom is conc...

Table of contents

• Cover
• Halftitle
• Title
• Copyright
• Contents
• Introduction
• PART 1. Electricity
• PART 2. Electronic Components
• PART 3. Electronic Systems
• PART 4. Electronic Systems in Action
• Supplements
• Acknowledgements
• Index