PHY II ESSAY REPORT

Wheatstone Bridge and Resistance

The 19th century was as very good era of discovery in electrical knowledge, and technology that laid the foundation for what we see today in our society. Scientist like Luigi Galvani for his work with frogs led to his discovery in 1781 of galvanic or voltaic electricity. Galvani found he could make the muscles of a dead frog twitch when he touched them with different metals or the current from a nearby static electric generator. Alessondra Volta for creating the first battery laid the foundation for many other great discoveries in this field. Some other great concepts that came later in 19th century was Ohms law, Electromagnetism, Faraday law, and many more.

A discovery of great significant was done by Samule Hunter Chrisite in 1833 and improved by Charles Wheatstone in 1843. This discovery used a device know as a wheat stone bridge, which gives a precise method to measure resistance against a known standard.

In the Wheatstone a comparative device measures two additional relative resistance from two separate resistors. The relative resistance equals the lengths of a divided wire wound in a coil of ten-turns within a potentiometer, a device allowing the manipulation of this resistant ratio. The goal of the this lab is to accurately use the methods created by the inventors by simulating their method in discovering this new phenomenon . In the lab we measured the electrical resistance using Wheatstone bridge, which was commonly used to measure unknown resistance in resistors. One variable resistor and unknown resistor are placed in bridge setup show in the figure below and adjusting the resistor current through a galvanometer until is made zero by using reading from a multimeter.

More precisely, Rx is not given and must be measured; the other three resistors are given and one of the resistors is adjustable. A ratio of the two given resistors is the same ration as the other resistor given and unknown. This happen because, voltage between the two points will equal zero; therefore, no current can flow between these points. This method allowed for very accurate reading which verify the method used to measure resistance and resistivity. Mathematically, if a bridge is working the current going through the galvanometer will be zero which establishes the concept that Resistor 1 (R1) + Resistor (R2) in parallel with Resistor (R3) + Resistor (R4). In addition, the setup illustrates the concept of using potential difference in order to determine the unknown for resistors, capacitance, inductance, and other values essential to circuit setups.

Two of the main concepts that came from the use of a Wheat stone bridge is the idea of resistance and resistivity. First, resistance is a criteria in the electrical circuit that can resist the flow of current; in addition, the resistance causes collisions on charged particles carrying a current with other particles that have a certain setup in the conductor. This is important, because the resistance depends on the material. That is why the Wheatstone bridge is so unique since it uses the resistance of a know resistor which is made up of material to avoid reactance in order to find the unknown resistance in the set up. The other component of a Wheatstone is the resistivity of a material which describes the conduct of current as result of an applied electric voltage. Also known as Electrical resistivity it is an intrinsic property that quantifies how strongly a given material opposes the flow of electric current.

The use of this technique to measure unknown resistance is very useful because it draws on the relationships of how current flows through certain materials based on their fundamental properties to increase current flow or decrease it based on finding a desired resistance; therefore, allowing for the creation of certain types of circuitry that can control the amount current needed to make electronic device perform a certain task.