PH - 262 / 11 Fall 2001

Engineering Physics II

Professor: Alvandi

Submitted By:

Andrew Buettner

Partner: Peter Fetterer

Lab #4: Electrical Resistance

Thursday, March 06, 2003

Table Of Contents

1) Cover Page...............................1

2) Table of Contents.....................2

3) Objective..................................3

4) Components Used....................3

5) Procedures................................3

6) Lab Data / Results.....................4

1) Table 1...........................................4

2) Diagram 1......................................4

3) Diagram 2......................................5

4) Diagram 3......................................5

5) Diagram 4......................................5

6) Diagram 5......................................6

7) Diagram 6......................................6

7) Answers to Lab Questions........6

8) Conclusions..............................8

9) Attachments..............................8

Objective

The objective of this lab is to investigate the relationship between current and voltage for several common electrical circuit elements. Then use this data to explain the behavior and effectiveness of resistance.

Components Used

1) Variable voltage power supply

2) 300W resistor

3) 500W resistor

4) Multimeter

5) Light bulb

6) GE Diode

Procedures

1) Assemble the following circuit:

2) Using V=1v - V=10v in 1v increments measure the current through the resistor.

3) Repeat step 2 using the 500W resistor.

4) Repeat step 2 using both resistors in series.

5) Repeat step 2 with both resistors in parallel

6) Replace the resistor with the light bulb and repeat step 2

7) Replace the bulb with the diode in a forward bias configuration.

8) Using voltages of .125V - .5V in .125V increments, find the current through the diode

9) Reverse the diode bias and repeat step 8.

10) Plot all information on graphs.

Lab Data / Results

1) Table 1: Voltage - Current Relationships

	240W	470W	Parallel	Series	Light
1.26V	4.99mA	2.62mA	7.34mA	1.74mA	345mA
2V	7.97mA	4.19mA	11.86mA	2.80mA	420mA
3V	11.97mA	6.28mA	17.7mA	4.19mA	492mA
4V	15.91mA	8.36mA	23.7mA	5.55mA	563mA
5V	20.1mA	10.52mA	31.1mA	6.99mA	626mA
6V	23.9mA	12.5mA	37.6mA	8.38mA	681mA
7V	28.3mA	14.8mA	44.0mA	9.75mA	735mA
8V	31.9mA	16.8mA	50.1mA	11.1mA	800mA
9V	36.4mA	18.9mA	56.6mA	12.6mA	840mA
10V	41.6mA	21.1mA	63.1mA	13.95mA	890mA

2) Diagram 1: Graph of V / I for 240W Resistor

3) Diagram 2: Graph of V / I for 470W Resistor

4) Diagram 3: Graph of V / I for Parallel Resistors

5) Diagram 4: Schematic 1, Enlarged View

6) Diagram 5: Graph of V / I for Series Resistors

7) Diagram 6: Graph of V / I for Light Bulb

Answers to Lab Questions

1) Q: Given a curved line and a straight line illustrating the relationship between voltage and current, which one is ohmic?

A: The one with the straight line.

2) Q: Given the lab illustration, what is the resistance of the ohmic material?

A: 1W

3) Q: For the same image, find the resistance at 2V, 4V, and 5V.

A: 2V -> .8W; 4V -> 1.33W; 5V -> 1.67W

4) Q: How does the resistivity of the material increase as the voltage increases?

A: The resistance increases.

5) Q:What is the equivalent resistance of two resistors in series?

A: R_T = R₁ + R₂

6) Q: Is R_T greater or less than the individual resistors?

A: Greater

7) Q: If R1 and R2 are both non ohmic, and their equivalent resistances were found independently, then they were put together, would their resistance remain the same, and explain why.

A: No, if they are non ohmic, then there is no linear relationship between the voltage and current, and the voltage would be divided between the two devices.

8) Q: What assumptions are made for ohmic materials?

A: That their resistivity is not dependent on temperature, pressure, or any other physical change.

9) Q: What are the units of aV/T, and are they unitless?

A: There are no units, the result is a scalar number with no properties assigned.

10) Q: What is the value of a/T at room temperature (Rounded Whole)?

A: a @ 55

11) Q: Find the equivalent resistance of a diode as a function of voltage.

A: dI/dV = e^^aV/T*a/T

12) Q: What is r at .125V, .25V, and .5V, why are the vlues so different? (Note: no current values were taken so R can not be found)

A: V = .125V : R = 5.13x10^-4W; V = .25V : R = .481W; V = .5V : R = 422KW There is a small current that still flows causing the resistance to change dramatically at low voltages.

13) Q: Does the Current / Voltage data from the diode support the equation I = I₀e^^aV/T equation, explain.

A: No data was taken that could support or refute this question.

Conclusions

From this lab Ohm's Law can be proven. For ohmic elements, the relationship between current and voltage is linear, and easily predictable. However, there were inaccurate values taken for both of the non-ohmic elements. The light produces inaccurate results because it's current draw was beyond the capabilities of the supply powering it. Also, no readings were made for the diode because there is no available power supply capable of generating safe voltages for the diode (Below 1V). The lowest voltage that can be produced with a conventional power supply (one designed around the LM317 or equivalent) has a minimum voltage of approximately 1.25V. Due to the constant voltage nature of the diode, there was no way of producing a suitable voltage, therefore readings were not taken.

Attachments

Original lab data
Calculations