How Can I Demonstrate Electric Forces Using a Van de Graaff Generator?

[RossMiller]

I need to perform a demonstration of electric forces. Something more substantial than weak static charge forces would be best. Could someone please help me by describing a practical way for me to put a charge onto something lightweight and then generate an electric field to move it back and forth. A way to make an electric field that has a variable and easily controlled magnitude and direction is what I am looking for. Thanks.

 

[berkeman]

I need to perform a demonstration of electric forces. Something more substantial than weak static charge forces would be best. Could someone please help me by describing a practical way for me to put a charge onto something lightweight and then generate an electric field to move it back and forth. A way to make an electric field that has a variable and easily controlled magnitude and direction is what I am looking for. Thanks.

Welcome to the PF.

One demo would be to show a naked CRT and explain how the electrons are boiled off of the cathode at the base of the neck, and accelerated through the electron gun lenses in the neck and out to the anode/face of the CRT. It's the electric field of the lens elements and the high + voltage of the anode surface that accelerates the electron beam enough to light up the phosphors coating the inside of the face at the anode. Pretty impressive acceleration!

One downside of this demo is that a naked CRT can expose some pretty high voltages, depending on how you package the demo. If you guard all the HV generating circuitry, the anode button and the neck endcap are pretty well insulated.

EDIT -- The x-y deflection of the electron beam to paint the picture on the CRT face is done with magnetic fields generated by currents in the deflection yoke, but the acceleration of the beam toward the face/anode of the CRT is all due to the electric fields generated by the high voltages in the electron gun and on the anode.

 

[jim hardy]

For a demo you want something visual that moves.
could any of these be refined?



http://www.scientificamerican.com/article/bring-science-home-static-electricity-attraction/

 

[DrZoidberg]

Here are a few more videos that might inspire you.

 

[alphy]

There are many ways to demonstrate the effects of electric forces, and it ultimately depends on the materials and equipment available to you. However, one practical way to create a strong and controllable electric field is by using a Van de Graaff generator. This device can generate a large static charge on a metal sphere, which can then be used to create an electric field that can move lightweight objects.

To perform the demonstration, you can start by charging the metal sphere of the Van de Graaff generator using a rubber belt or similar material. Once the sphere is charged, you can place a lightweight object, such as a piece of paper or a small balloon, near the sphere. The electric field from the charged sphere will attract the object, causing it to move towards the sphere.

To demonstrate the direction and magnitude of the electric field, you can vary the distance between the object and the sphere, as well as the amount of charge on the sphere. By increasing or decreasing the distance, you can show how the strength of the electric field changes. Additionally, you can add or remove charge from the sphere to demonstrate how the direction of the electric field can be reversed.

Another way to demonstrate electric forces is by using a Leyden jar. This is a simple device that consists of a glass jar filled with water and a metal rod inserted through a cork stopper. By charging the metal rod with a static charge, you can create an electric field that can also attract lightweight objects, such as small pieces of paper.

In conclusion, a Van de Graaff generator or a Leyden jar can be effective tools for demonstrating the effects of electric forces. By varying the distance, charge, and materials used, you can create a demonstration that showcases the strength, direction, and variability of electric fields.