Day 53: Circuit to Measure Capacitance

Today, AP Physics 2 students start an extended lab to model the characteristics that determine the capacitance of a parallel plate capacitance. Before they can do that, they need a way to measure the capacitance of a capacitor. I shared with students a simple circuit I saw at the local AP Summer Institute from Patrick Polley that produces a signal whose period is proportional to the capacitance of the capacitor. For know student will treat this circuit as a black box; in the next unit, they will understand how it works. Students needed some time to brush up on their breadboard and circuits skills. So, they only had time to build the circuit not use it. We will build it again tomorrow!


  ##paradigmlab ##electrostatics  

Day 52: Electric Potential Surfaces

Today, AP Physics 2 explored the resulting visual from yesterday’s mapping electric potential lab. We focused on visualizing the electric potential surface and continued to make an extended analogy between electric potential surfaces and equipotential lines and topographic maps and contour lines. Finally, we connected the magnitude of the electric field to the “steepness” (really gradient) of the electric potential surface.

I shared how an elevation plot of the electric potential surface can help visualize the electric potential and electric field. I shared xkcd’s Gravity Wells poster as an example of an elevation plot for gravitational potential.

The 3D electric potential plot of the conducting sheet with the closed conducting surface in the middle turned out fantastic. I nicely demonstrated that the electric potential within the closed conducting surface is constant and, therefore, the electric field is zero.

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  ##electrostatics ##representations  

Day 51: Mapping Electric Potential Lab

Today, AP Physics 2 students completed the Mapping Electric Potential Lab from Vernier’s Advanced Physics Beyond Mechanics lab manual. I purchased a conductive pen this year and modified on of the conductive sheets with parallel plates to include a closed conducting surface in the middle of the sheet. The 3D and 2D potential plots captured by the students look excellent. I’m especially interested in how the one with the closed conducting surface looks.

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