# What causes resistance? Lab

#### Teacher Notes

Four labs can be conducted using the materials in the Resistance Board and Ohm’s Law kit:

• the effect of length on resistance (using the Pencil Lead Resistance Board)
• the effect of different materials on resistance (using the Pencil Lead Resistance Board)
• the effect of wire diameter on resistance (using the Wire Resistance Board)
• the effect of voltage on the current in a resistor (using the Ohm’s Law kit)

Use the Resistance Boards Kit for this activity.

#### Part 1. The Effect of Length on Resistance

Note: A summary of this lab is presented below;

#### Purpose

How the resistance of a resistor vary with its length?

#### Materials

• Four alligator clip wires
• A digital multimeter

#### Directions

1. First, brainstorm with your group about factors that can affect the resistance of an object. Discuss whether each factor has a direct or inverse relationship with resistance; for example, “resistance increases as ________ increases/decreases.”
2. In this activity you will use a pencil lead as a resistor. Fasten the HB pencil lead in place by sliding it under the clamps of the Fahnestock clips. Be cautious; the lead breaks rather easily.
3. Connect the circuit. Draw a diagram. Use a colored pencil and arrows to trace the path of electrons in the circuit shown.
4. Part A: Use the HB lead. Design and conduct an experiment to determine the effect of the length of the pencil lead on the resistance measured.
5. What factors are held constant in your experiment?
6. Procedure:
7. Make a data table. Conduct your experiment, and record your results: