Basic Electricity

BASIC ELECTRICITY AND ELECTRONICS

EMISSION OF ELECTRONS

Introduction

The movement of electrons constitutes the flow of electric current. Electrons are negatively charged particles which move around the nucleus of an atom. There are forces of attraction between these electrons and the nucleus of the atom. This helps to keep the electrons in their shells.

If that is the case, then how can an electron overcome these forces and break away from its nucleus to constitute current flow? The answer to this question is the subject of the unit.

You will be introduced to matter and the structure of the atom before looking at how electrons are liberated from a material; a phenomenon electronic engineers are very much interested in. The unit will end with a look at application of emission of electrons in the design of one of the first electronic components known as a valve or vacuum tubes.

Objectives

After studying this unit you will be able to

Explain what matter is

* describe the structure of an atom

* explain the various methods of emission of electrons

* describe the construction of discharge lamps

* describe the operation of valves

* state the applications of the various valves

MATTER

The definition of matter in common use is that, matter is anything that has mass and volume (occupies space). For example, a table, a stone etc. All these examples occupy space and have mass and so they can be said to be made of matter. Scientifically, however, matter may be defined as what atoms and molecules are made up of. This means that anything made of protons, neutrons and electrons is “matter”. This definition is based on the physical and chemical structure of matter (Walker and King 2005).

Matter exists in several states or phases (State of aggregation). This depends on ambient pressure, temperature and volume.

Phase: a form of matter having a relatively uniform chemical composition and physical properties like density, specific heat etc.

The most...