# Physics Ohm Law

Topics: Electric current, Electrical resistance, Ohm Pages: 5 (457 words) Published: April 15, 2014
﻿Experiment No: EM-1Title: Ohm’s Law, Meters, Resistivity I Purpose:
The basic of simple electrical circuits and measurements is learned. Also, investigating the dependence of the resistance of a wire on its length, cross-sectional area, and the material of which it is made. By examining electrical resistance (R) through a metal conductor, the voltage (V) and current (I) through the conductor, the following principles will be demonstrated: 1.) Ohm’s Law

2.) Dependence of resistance (R) on the length (L), cross-sectional area (A) and electrical resistivity (ρ) and volt, (V). II Procedure:
Apparatus: DC power supply, milliammeters and ammeters, voltmeters, SPST switch, a “fused” connector, a 2-meter slide wire resistance, and mounted resistance spools. Variation of V and I, with R held constant

1 Connect the apparatus as shown in the Figure below, attaching the voltmeter last.

Figure 1

2 Set the power to 4 volts. To begin with, set the voltmeter on the 0-5 volt rang and the milliammeter on the 0-1000 ma range. 3 Take a series of simultaneous voltage and current readings for currents I: 75, 150, and 225 milliamps. 4 Create a table and observe the value of the resistance and see if there is any constant. Variation of V along a resistance wire, I constant

1. Connect the apparatus as shown in the Figure below.
Figure 2

2. Measure of V across various lengths L of the 2-meter wire between the 0 cm end and other points where the KEY is placed. 3. Measure and record the voltage V and the current I for lengths L of 20 cm, 50 cm, 80 cm, 120 cm, 150 cm, and 200 cm. 4. Calculate the resistance R, using Ohm’s Law for the length of wire for each case, and add the results to a table. 5. Graph the R’s versus the L’s.

III Data/Calculations/Results

Variation of V and I, with R held constant
I1= 75 milliamps
V= 0.52 volts
I2= 150 milliamps
V= 1.03 volts
I3= 225 milliamps
V= 1.70 volts

Variation of V along a resistance wire, I constant
L= 20 cm
I= 34 amps
V= .26 volts
L= 50 cm
I= 38 amps
V= .68 volts
L= 80 cm
I= 40 amps
V= 1.12 volts
L= 120 cm
I= 40 amps
V= 1.72 volts
L= 150 cm
I= 40 amps
V= 2.14 volts
L= 200 cm
I= 40 amps
V= 2.80 volts

Graph 1

-This graph depicts the difference between resistance versus length. The slope of the line is 0.3495 cm. The best fit line is y=0.3495x + 0.561. IV Summary of Results/Conclusions:
The data found by using the apparatus shows how the current and voltage produces certain resistance at different currents and lengths by the use of the KEY. The calculations and graph depict the increase in the line as show is due to the effect that each current is ran at certain high lengths. This in conclusion shows how Ohm’s Law is in play when finding the resistance in both parts of the lab.