03/23/2011

Abdullah Alsaffar

Nate Wyse

Resistance Lab Report

Introduction and Theory

The purpose of this lab is to test the efficiency of Ohm’s law by calculating

the resistance of different resistors. Also, to study the temperature of a light

bulb when current flows through it and calculate that temperature.

The resistance of a resistor can be calculated using Ohm’s law:

R=I/V (1)

Where, R = Resistance ()

V = Voltage (V)

I = Current (A)

If we can measure the current and the voltage across a resistor in the circuit

board then the resistance is easy to calculate, the resistance in this case is

also the slope of a plot of Current Vs. Voltage, which is used in this lab

report and included in the Graphs section.

In order to calculate the temperature of a light bulb when current goes

through it, we need to study the temperature and the resistivity of the light

bulb. So the resistance of a light bulb is given by the following equation:

R = L / A

Where L = length of the cord (m)

A = Cross-sectional area of the wire (m2)

And the temperature can be found by the following equation:

R = R0 ( 1 + a( T – T0 ) ) (2)

Where R = Resistance in room temperature ()

a = The temperature coefficient of resistance = 0.0045 C-1

T = Temperature of the light bulb in oK

T0 = Room Temperature in oK

Procedure

The procedure is divided into three different parts. The first part is to

calculate the resistance of different resistors across a circuit board using a

power amplifier and Data Studio “ A computer program used to initialize the

lab” We wanted to study the resistance when we produce different voltages

using the power amplifier. So we produced voltages that ranged from 5 V to

1 V and recorded our data and calculated the resistance. See graph and data

below.

Then we set the voltage at 2.5 V and measured the resistance again but with

different frequencies. Data, graphs, calculations of every recorded data is

given below in their sections.

In the third and last part of the laboratory, we needed to find what happens

to the temperature of a light bulb undergoing a current flow, and to calculate

the temperature using equation 2 given in Introduction and Theory part of

this lab report. We set the voltage at a constant rate of 4.5 V and then

measured on high, medium, and low frequencies. Graphs are given below.

Data and Graphs

Please look at graphs and data, which are labeled in which they were

described in the lab report.

Calculations and Results

For part I we needed to calculate the resistance using Ohm’s law after

measuring the current and the voltage that goes across a resistor.

Using equation 1:

R = I / V = (0.15 A) / (5 V) = 33.33

Other calculations are also accurate and done with excel are on separate

papers.

Conclusion

In conclusion we studied the resistance of resistors across a circuit board

using Ohm’s law, and then using the characteristics of a light bulb we

calculated the resistance of a light bulb in order to successfully calculate the

temperature when a current is currently flowing in a light bulb.