Massachusetts Institute of Technology
Sign in

Adjustable Capacitor with Dielectric

First, an adjustable parallel-plate capacitor is held at a constant voltage. As the separation between the plates is widened, the electrometer shows charge (or current) flowing off of the plates, while the electroscope shows no change in voltage. Notice (by the deflection of the needle) that more charge flows off of the plates when they are closer together, and less when further apart. When the plates are brought back together, we see charge flowing back onto of the plates.

Next, we deposit a fixed amount of charge onto the left plate. Now, when the separation is widened, the electroscope shows a rising voltage, even as the amount of charge stays constant. When a block of plexiglass (a dielectric) is inserted between the plates, the voltage drops. However, when the plexi is removed, the voltage rises back up again, showing that the charge is still there.

This is one of the main reasons capacitors are built with dielectrics between their plates; more charge can be stored at a lower voltage.

Comments (1)

insert here

Posted over 2 years by Anonymous 00:00:24

You need to log in, in order to post comments.

February 20, 2009 09:52
Creative Commons Attribution-NonCommercial (What is this?)
Additional Files

38842 times

More from MIT Department of Physics Technical Services Group

MIT Physics Demo -- Microwave Interference

MIT Physics Demo -- Microwave Inter...

Added over 8 years ago | 00:02:11 | 29997 views

Orbital Motion

Orbital Motion

Added over 7 years ago | 00:03:00 | 46137 views

MIT Physics Demo -- Jacob's Ladder and the Melting Nail

MIT Physics Demo -- Jacob's Ladder ...

Added over 8 years ago | 00:01:26 | 57169 views

MIT Physics Demo -- Centrifugal versus Centripetal Motion

MIT Physics Demo -- Centrifugal ver...

Added 8 years ago | 00:01:18 | 37091 views

Relative Motion Gun

Relative Motion Gun

Added over 7 years ago | 00:01:07 | 56890 views

Faraday's Cage

Faraday's Cage

Added over 7 years ago | 00:01:23 | 67704 views