Student handout: Electric Potential of Two Charged Plates

Students examine a plastic "surface" graph of the electric potential due to two charged plates (near the center of the plates) and explore the properties of the electric potential.
• group Small Group Activity schedule 30 min. build Yellow plastic surface, Big Whiteboard (1 per group), Contour map for a parallel plate capacitor in a plastic sleeve (1 per group), Ruler (1 per group), Dry-erase pens and erasers (1 each per student), Student handout (1 per student) description Student handout (PDF)
What students learn
• How to interpret a surface plot (plastic surface model) of the potential due to a parallel plate capacitor
• The potential near the center of two charged plates is a plane (constant slope)
• Equipotential curves represent a single value of potential
• Equipotential curves for the center of two charged plates are equally spaced horizontally
• The height of zero potential is arbitrary/chosen for convenience

Before you is a plastic surface representing the electric potential between two charged plates. A $1~cm$ height difference corresponds to an electric potential difference of $1~V$.

Interpret the Surface
Rank the three points by the value of the electric potential from greatest to least.

Mark three points on the surface that are separated by equal (non-zero!) changes in potential.

Identify (and mark) all the points with the same value of potential as your three points. What patterns do you notice?

Connect Representations
Align your surface with your contour map. How are you making this alignment? Where is the surface a good approximation of the potential? Where is the approximation less good?

Generate a Graph
Sketch a graph of the potential ($V$) vs. distance from the negative plate ($x$).

• Describe the relationship between potential and distance from the negative plate.
• Propose an equation to describe the electric potential as a function of the distance, $x$, from the negative plate. Where did choose for the location of $V=0$?

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Learning Outcomes