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 (2-11), a range commonly used in many practical experiments.