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## Conductors: Instructor's Guide

### Main Ideas

Students explore the properties of conductors.

Estimated Time:

Students work in small groups to solve Griffiths Problem 2.36

### Activity: Introduction

Short lecture on the properties of conductors, following Griffiths Section 2.5.

1. $E=0$ inside a conductor
2. $\rho=0$ inside a conductor
3. Any net charge resides on the surface
4. A conductor is an equipotential
5. $E$ is perpendicular to the surface just outside a conductor

### Activity: Student Conversations

• Charges are free to move – This is a surprisingly difficult problem for students. Many students do not try to reason about charges moving, which is where all of the properties come from.
• Charges distributed on the surface – Many think that the charge is distributed on the surface (instead of the charge polarizing the conductor).
• Overgeneralizing the “balancing” – Some groups overgeneralize the idea of fields “balancing” and thought that the field inside the cavities would be zero.

### Activity: Wrap-up

Students also had a difficult time at the end of the activity articulating what they had learned from this problems, so there was an assigned homework problem that asked them to do so.

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