DESIGN AND CONSTRUCTION OF A VARIABLE RESISTANCE BOX

ABSTRACT

In this project a resistance box has been constructed using locally available materials namely, 1/3 and plywood for the construction of the box, cupper wire, Ferro board, soldering iron, soldering lead, screw and resistors.

The resistance obtainable from the box ranges from 2-11W. The box is fitted with terminal s to allow easy use in physics laboratory practical. At the end of the experiment, the values obtained are very close to those obtainable using imported box.

TABLE OF CONTENT

Title page                                                                                         i

Certification                                                                                     ii

Dedication                                                                                       iii

Acknowledgment                                                                                      iv

Abstract                                                                                           v

Table of content                                                                              vi

CHAPTER ONE

1.1    Introduction                                                                            1

1.2    Aim of the project                                                                  2

CHAPTER TWO

2.1    Resistor                                                                                  3

2.2    Theory of operation                                                              4

2.3    Classification of resistors                                                     7

2.4    Factor affecting resistances                                                          12

2.5    Reactivity and conductivity                                                  13

2.6    Resistor colour codes                                                           15

2.7    Symbols of resistor across battery                                               17

2.8    Uses of resistors in a circuit                                                 19

CHAPTER THREE

3.1    Design and construction                                                      20

3.2    Other components of the box                                              21

CHAPTER FOUR

4.1    Test and experiments                                                           23

4.2    The box in a simple circuit                                                   24

4.3    Discussions                                                                           26

CHAPTER FIVE

5.1    Summary                                                                               27

5.2    Conclusion                                                                                      28

5.3    Recommendation                                                                 29

References                                                                                     30

CHAPTER ONE

1.1    INTRODUCTION

In many electrical measurements, standard variable resistances are required. These standard resistances come in various forms and shapes. The resistance box is one of them.

These resistance boxes are imported and in most cases very expensive. Most schools can therefore not afford to buy enough for the use of there students. It is therefore important for technologists to be able to improvise using locally available materials.

Also, during the course of designing and construction, student technologists are really exposed to more practical works in order to acquired a lot of experience on how to make use and handle many laboratory tools, equipments and apparatus.

We have two different, types of resistance boxes which includes:

(a)     Decade type

(b)     Plug type

In decade type, the coil of each resistance are connected in series, and there is a rotary switch which also aids in contact with each other. The switching used are of high quality compared with the resistance of the coils which they are selected.

In plug type, no switches are required instead, their resistance is varied by means of plugs. The resistance coils are formed across gaps with a thick brass bar, and the gaps are formed in the holes being drilled to receive the short circuiting plugs.

1.2    AIM OF THE PROJECT

This project aim at presenting precisely the process of construction of a resistance box, which is an imported equipment in the physics laboratory.

Most practical work involve the use of resistors of fixed value that are fixed into and later removed from the circuit. The replacement of a particular resistor of a given value may lead to destruction of the resistor so an alternative way for guiding against this is by use of variable resistance box.

This resistance box is to provide a resistance range between two and eleven (2-11W), a range commonly used in many practical experiments.