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

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

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

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

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: RT = R1 + R2

6) Q: Is RT 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

1. Original lab data

2. Calculations