ELEC 101

Prof. Rich Kozick

Prof. Rich Kozick

Resistors: Measurement, Color Code, and Design

where d and A are the thickness and cross-sectional area of the material, respectively. The resistivity, an intrinsic property of the material of which the resistor is composed, is large for good insulators and small for good conductors (Table 1).

Table 1: Resistivity of Conductors and Insulators |
|||

Material |
Resistivity at 0 |
Resistivity at 22 |
Classification |

Silver |
1.47 |
1.61 |
Conductor |

Copper |
1.55 |
1.70 |
Conductor |

Gold |
2.05 |
2.20 |
Conductor |

Aluminum |
2.50 |
2.74 |
Conductor |

Ceramic (Porcelain) |
- |
10 |
Insulator |

Plastic (Acrylic) |
- |
>10 |
Insulator |

Combinations of Resistors:

When n resistors are connected in series (end to end), the
equivalent resistance, R_{eq}, of the series combination of
resistors is the sum of the individual resistances such that where R_{i} is the
resistance of the i^{th} resistor. (Note: Elements in series
have the same current through them.)

When n
resistors are connected in parallel, the equivalent resistance,
R_{eq}, of the parallel combination of resistors is the sum of
the individual resistances such that where R_{i} is the resistance of the i^{th}
resistor. (Note: Elements in parallel have the same voltage across
them.)

- Complete the E-lesson on measuring resistance as follows.
Record the steps for measuring resistance with the
digital multimeter (DMM)
in your lab notebook for future reference.
- Start the E-lesson by clicking on the link:

`http://www.facstaff.bucknell.edu/mastascu/eLessonsHTML/EEIndex.html` - Go through the E-lesson on resistance by clicking on "Elements" and then the first item under "Resistors."

- Start the E-lesson by clicking on the link:
- For information on resistor color codes and an interactive program to determine a resistor's value, see the following links. (These are linked to the Laboratories page on the course web page.) You may want to print the color code description and paste it into your lab notebook for future reference.
- Design a network of resistors and switches according
to the following description.
Study the circuit below. It has five resistors:

**R1, R2, R3, R4, R5**and four switches**S1, S2, S3, S4**. These switches can be opened and closed to control the current**i**. In a more advanced system, a computer could be used to turn on and off various switches in sequence to control the current in the circuit.** WE WILL NOT USE ACTUAL SWITCHES; JUST USE WIRES TO CLOSE SWITCHES. **

*one*set of resistor values that can be used with various switch settings such that the following set of currents can be selected. Only use resistors that have values of 1 K ohm or greater.- 0.25 mA
- 0.33 mA
- 0.50 mA
- 0.67 mA
- 1.00 mA
- 2.00 mA
- 2.50 mA

Record your calculations and circuits in your lab notebook. Also, record the resistor values and the switch settings required to obtain each of the desired currents in your lab notebook.

Measure the resistance of the circuit that you designed for each of the switch settings using the ohmmeter setting on the DMM.

You do not have to connect the 5 V source or measure current. Please measure the equivalent resistance of your network for various switch settings, and use Ohm's Law to determine the current that would result with a 5 V source.

Resistor Color Code Description:

`
http://www.eg.bucknell.edu/~bsprunt/classes/references/resistor_color_codes/resistor_color_codes.htm
`

Resistor Code Calculator:

`
http://www.eg.bucknell.edu/~bsprunt/classes/references/resistor_values/resistor.htm
`

Thank you.