CONSTRUTION OF METTER BRIDGE IN OUR LABORATOR
The working of a meter bridge is based on the principle of Wheatstone bridge. It uses two resistances instead of four resistances obtainable in a Wheatstone bridge. The construction of the meter bridge was simply the selection, assembling and wiring of the components, by following the circuit diagram, into the find piece. The constructed bridge is tested and demonstrated to find the value of unknown resistance. One good thing about meter bridge is that, it is simple and more accurate than Wheatstone bridge. This is because the unknown and known resistances can be changed in a continuous fashion.
Our ability to measure a quality determines our knowledge of that quantity, the measurement of electrical quantities or other parameters in terms of electrical quantities is essential to our everyday life. Hence there is need is to have a through knowledge of electrical instrumentation and measuring systems.
Instrumentation is the technology of measurement in all branches of sciences, engineering and technology and are mainly use to monitor a process or operation as well as controlling (victor, 2009). However the term instrument in its wider sense may be categorized as indicating, recording and controlling instruments. As it concerns the topic of our research, indicating instrument is to be intensively considered. Indicating instruments are those instruments which indicate the value of the quantity that is being measured at the time at which it is measured. Such instrument according to Theraja (2000), consist essentially of a pointer which moves over a calibrated scale and which is attached to a moving system pivoted in jewelled bearings. These indicating instruments are Ammeter, voltmeter, wattmeter, galvanometer, meter bridge etc which measures current, voltage, power, smaller values of currents and resistances respectively.
Our interest this work is to construct a meter bridge that will be useful in the laboratory. To achieve this target requires a consideration and understanding of the principle of operation of a Wheatstone bridge and a potentiometer.
In the simplest definition, a meter bridge is simple type of potentiometer which may be used in school science laboratories to demonstrate the principle of resistance measurement by potentiometric means (Jan, 2013).
To construct a meter bridge involved the selection of various components and the connection of these parts into the workable system. These components like galvanometer, connecting wire, meter bridge rule, jockey, cell, key are discussed in next subsequent chapters.
This material is thus divided into five chapters beginning with chapter one which introduces the concept of work and ends in chapter five which contains conclusion, recommendation and the references.
1.1 Historical Background
The discovery of the meter bridge was as a result of the modification of the Wheatstone bridge. Thus, the working of meter bridge is based on the principle of what stone bridge. It is well known that the first user of the bridge circuit was Samuel Hunter Christie in 1833 (Thomas, 2005). Wheatstone acknowledge this in his Bakerian lecture. For many years it has been assumed that Christie was the son of William Christie of the eponymous auction house, but recently it has become clear that he was the son of a different William Christie.
Without the presence of a standard cell, the bridges can not work or produce results. The original design of a standard cell is due to the british engineer Latimer clark, Ca. 1878. The idea, according to Thomas (2005) was to make a reproducible standard of EMF that could be used for positional work in electricity. The original design used zinc and mercury electrodes immersed in zinc and mercury sulphate. The English-America inventor and electrician, Edward Weston (1850 – 1936), patented an improved standard cell in 1893 that replaces zinc with cadmium. This cell’s EMF changed very little with temperature, and it had a characteristic EMF of 1.0183V at 200C.