Design And Construction Of A Variable Resistance Box

Project and Seminar Material for Physics

Design And Construction Of A Variable Resistance Box


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 2-11Ω. 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
  • Certification
  • Dedication
  • Acknowledgment
  • Abstract
  • Table of content

Chapter One

  • 1.1 Introduction
  • 1.2 Aim of the project

Chapter Two

  • 2.1 Resistor
  • 2.2 Theory of operation
  • 2.3 Classification of resistors
  • 2.4 Factor affecting resistances
  • 2.5 Reactivity and conductivity
  • 2.6 Resistor colour codes
  • 2.7 Symbols of resistor across battery
  • 2.8 Uses of resistors in a circuit

Chapter Three

  • 3.1 Design and construction
  • 3.2 Other components of the box

Chapter Four

  • 4.1 Test and experiments
  • 4.2 The box in a simple circuit
  • 4.3 Discussions

Chapter Five

  • 5.1 Summary
  • 5.2 Conclusion
  • 5.3 Recommendation
  • References

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:

  1. Decade type
  2. 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.

Chapter Five

Summary and Conclusion

5.1 Summary

The summary of what had been done so far in this project report include the introduction, aim of the project, description of method employed which is connecting type. The theoretical background is this explained i.e resistivity and conductivity, classification of resistors, resistors colour code etc Design and construction of the variable resistance box. It is constructed and explained, highlighting the choice of material used and the constructional precaution.

Two tests are carried out, involving the used of digital multimeter and comparison between the constructed and the imported box. The basic principle of this project work is ohm’s law, which states that “At constant temperature the amount of current flowing through a metallic conductor is directly proportional to current in voltage i.e. V = IR
Two tests have been carried out with this constructed box. One was to check the accuracy of the various resistance values obtainable from the box. Within the constructed range (2-11) the value obtained from the box are vary close to the values indicated on the box using a multimeter.

5.2 Conclusion

A variable resistance box had been constructed in this project work which is of importance to the student that undergoes physics course. The resistance box plays an importance role in electrical and electronics circuit in order to obtained varied required values of resistance in a circuit.

The method used for the resistance box constructed in this project is the terminals type which is considered to be more accurate with minimal error.

By comparing the laboratory standard value and the constructed box, it can seen that both physical, instrumental and human errors are minimal. I will now conclude that, the constructed resistance box within the experimental error is accurate enough for most laboratory experiments.

5.3 Recommendation

Taking all the necessary precaution, this models constructed can further be improved so that the error can be minimized to ± 1%. Also, this locally made resistance box would be more adequately used in our institutions of learning and for commercial purposes and to minimize the cost for the equipment.

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