Demos: 5A-16 Electric Potential Proof Plane
A proof plane is connected to a projectable electrostatic voltmeter rated at 0-300 V. The Van de Graff electrostatic generator is started and the proof plane taken near it. A voltage is registered by the voltmeter indicating a potential associated with the electric field. A potential difference is evident when the proof plane is moved along a radius. The closer the proof plane is to the sphere, the higher the voltage reading.
Directions: Be sure the voltmeter is zeroed and the proof plane initially grounded. Start the generator and place the proof plane several meters away. Then slowly move along a radius and keep an eye on the voltmeter.
Suggestions for Presentation: Electric fields and potentials are attributes of the space surrounding a charge and are not observed "directly." Although the workings of the ESV are not evident, point out that it is designed to measure potentials. Ask the students how the potential is expected to change as the proof plane is moved to various locations relative to the charge.