Essay Ohm ' s Law and Resistance

OHM’S LAW AND RESISTIVITY-RESISTANCE
Nan Li De La Salle University
2401 Taft Avenue,Manila, Philippines 1004
Jimmy4everonly@gmail.com

Abstract When the resistance of a metallic conductor is considered constant the relationship between voltage and current is a linear relationship which means voltage is directly proportional to the current when resistant is constant. When the maintaining current is considered constant the relationship between voltage and resistance is a linear relationship which means voltage is directly proportional to the resistance when current is constant When the voltage is considered constant the relationship between current and resistance is not linear relationship the plot of current an VS resistance is a hyperbolic graph which means the current is directly proportional to the 1 over resistance (or inversely proportional to resistance), when voltage is constant. The resistance of a metallic conductor has been found to be directly proportional to the length of the conductor and inversely proportional to its cross-sectional area.

Introduction According to Georg Ohm, in 1826, observed that current I through an electrical conductor is always directly proportional to the potential difference (or voltage) V across the conductor. Electrical conductors that obey Ohm’s law, those that demonstrate linear relationship between I and V, are said to be ohmic. Most metals are ohmic conductors. It was found out that not all materials obey Ohm’s law; such materials are considered to be nonohmic conductors. A semi conducting pn junction diode is an example of a device that does not obey Ohm’s law. The resistance of an electrical conductor, whether it is ohmic or nonohmic, can be determined by measuring the current I through the device when a potential difference V is applied across it. The resistance of the conductor is then R = V/ I
The unit of resistance s the ohm (W), potential difference is the volt , and current is the ampere . According to Ohm’s Law, there is a linear relationship between voltage V and current I when the resistance R of a metallic conductor is considered constant. V [pic] I when R = constant When the resistance R in a simple circuit is varied while maintaining current I constant, the voltage V across the resistor changes linearly with the resistance. V [pic] R when I = constant Consider a simple circuit in which the voltage across the variable resistor is maintained constant while resistance R is varied. From equation 1, we can deduce that the greater the resistance of a resistor the smaller the current I that will pass through it, assuming that the same voltage V is applied. Thus, I [pic] 1/R when V = constant

The resistance of a metallic conductor has been found to be directly proportional to the length L of the conductor and inversely proportional to its cross-sectional area A. The constant of proportionality is called the resistivity r of the material from which the resistor is made. In equation form, R = (ρL) /A
The resistivity of a material is considered constant at a constant temperature. The SI unit for length is meter (m); for area, square-meter (m^2); and resistivity, ohm-meter (Wm)
So we have the following objectives :
1. To be able to describe seats of emf
2. To be able to differentiate between emf and terminal voltage
3. To be able to state the significance of internal resistance and how this contrasts a real battery from an ideal battery
4. To be able to measure a battery’s emf
5. To be able to experimentally show the variation of a battery’s terminal voltage with its current output and from this calculate a battery’s internal resistance

Methodology
This experiment involved four parts, before the start of the experiment ,it has the PRELIMINARY work :
1. With the VOM set to Ohmmeter function, check the continuity of all the wire

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