# 3. Electric Fields and Discrete Charge Distributions

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## Learning Objectives

• To be able calculate the electric field at every point in space given a set of point electric charges and their locations.
• To comprehend the various ways in which we charge objects and explain them in words.
• To comprehend the nature of the electric field of an electric dipole and to recognize what is meant when we go to the limit of a perfect point dipole.
• To be able to describe why we put so much emphasis on the properties of electric dipoles.
• To be able to describe when an electric dipole immersed in an external electric field will experience a torque and a force.

## Preparation

### Course Notes

Read through the course notes before watching the video. The course note files may also contain links to associated animations or interactive simulations.

Coulomb's Law (PDF)

## Lecture Video

### Video Excerpts

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## Learning Activities

### Guided Activities

Read through the class slides. They explain all of the concepts from the module.

Slides (PDF)

### Self-Assessment

Do the Concept Questions first to make sure you understand the main concepts from this module. Then, when you are ready, try the Challenge Problems.

Concept Questions

Concept Questions (PDF)

Solutions (PDF)

### Challenge Problems

Challenge Problems (PDF)

Solutions (PDF)

## Problem Solving Help

Watch the Problem Solving Help video for insights on how to approach and solve problems related to the concepts in this module.

### Problem: An Electric Dipole

We have a charge +q located at aî on the positive x-axis, and a charge –q located at -aî on the negative x-axis. Find the electric field everywhere in space. Using your general expression, find the electric field at a distance r»far from the origin. Show that at this distance the electric falls off as inverse r cubed.

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» iTunes U (MP4 - 46MB)
» Internet Archive (MP4 - 46MB)

## Related Visualizations

The visualizations linked below are related to the concepts covered in this module.

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