Download Ohm's Law and Resistor Circuits Laboratory Experiment and more Lab Reports Physics in PDF only on Docsity! 17 V I R= ⋅ ( )1 Physics 2049C Laboratory 3 Ohm's Law and Resistor Circuits Purpose Part A. You will test Ohm's Law and apply it to a carbon resistor. Part B. You will analyze a circuit with resistors in series and deduce the equivalent resistance of these resistors in the circuit. Part C. You will analyze a circuit with resistors in parallel and deduce the equivalent resistance of these resistors in the circuit. Apparatus DC power supply, 340 S (or 350 Ω) rheostat, resistor board with three resistors, connecting wires, multi-scale ammeter, multi-scale voltmeter, linear graph paper (supplied by student). I. Preliminary Discussion Ohm's Law states that for an "ohmic" conductor, the voltage V across the conductor is directly proportional to the current I through the conductor. where the constant of proportionality is known as the resistance R. This proportionality should be intuitively obvious, as the greater the voltage ("electrical pressure") across a conductor, the more current ("electrical flow") you can push through it. The linear relationship for an ohmic conductor only holds when the temperature is held constant, as the resistance of a conductor increases with temperature. However, when a current flows through a conductor, energy is dissipated in the conductor as heat (this is known as Joule heating, given by P = I2R). Therefore, if too much current flows through a resistor, the resulting heat will increase the resistance, and the resistor will behave non-linearly and therefore not according to Ohm's Law. For this reason and because of a lack of experimental understanding among his contemporaries, Georg S. Ohm, a German physicist, was called a "charlatan" when he first published his law in 1827 (in Mathematisch Berichte) and it was not accepted until many years later. 18 II. Experiment A. Measuring the Resistance of a Carbon Resistor Using Ohm’s Law • Wire the circuit as in Fig. 1, using one of the three carbon resistors for the unknown Rx. • The 340S rheostat is connected as a "voltage divider". By moving the rheostat wiper, the voltage across Rx can be varied from 0 to 5 V. With the voltmeter and ammeter connected as in Fig. 1, record the voltage across Rx and the corresponding current through the resistor for at least 5 different voltages across Rx. • Plot the data on linear graph paper with current on the abscissa and voltage on the ordinate. Draw a "best fit" straight line through your data. • From your V vs. I plot, determine the resistance of R and compare it to the value of the measured resistor given by the color code shown in Fig. 2. (NOTE on Resistors: Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Gray=8, and White=9; Silver=10% and Gold=5%.)
