Tutorial details

Section I: Coulomb’s law

This section begins with a brief introduction to Coulomb’s law. Students consider a system of two different positive charges and are asked about the direction and magnitude of the forces between them.

In Questions D-E, students discuss how the force on a point charge changes when the charge separation or charge magnitude is doubled.

Section II: Superposition

Three $+Q$ charges are held in place along a semicircle with a $+q$ charge at the center. Question A involves a sample student dialogue about the vector sum of the forces on $+q$.

In Question B, students rank the magnitude of the net force on a charge $+q$ in three different situations. This ranking requires qualitative thinking about Coulomb’s law and the use of superposition.

Section III: Distribution of charge

In Question A, students compare the net force on a $+q$ charge in two cases. In one case the force is due to a small ball with charge $+Q$, and in the other a uniformly charged rod with net charge $+Q$.

In Questions B-D, students consider a series of experiments that involve a semicircular charged rod and point charges. They are asked about the forces on a point charge $+q$ due to the other objects and use superposition to reason about the net force.

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Prerequisite tutorials

The Newton's second and third laws tutorial is a prerequisite to Charge.

Other prerequisites

Familiarity with Coulomb’s law is not assumed. Facility with free-body diagrams and in applying Newton’s second and third laws is required.

Equipment

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• tutorial instructor slides
• tutorial student slides or worksheet

Discussion