Please Help. I have a question about an electroscope

[Curt Searcy]

I have been having a problem with the experiment entitled "How Do Different Materials React to Static Electricity". When I get to step 11 after "creating static electricity" by rubbing the balloon on the styrofoam plate and then place the electroscope onto the plate, there is no reaction from the foil ball. However, if I place the balloon near the foil, the foil is attracted to the balloon and moves towards it. I hope someone can tell me what it is I am doing wrong. Thank you for your help.

[ChrisG]

Hi Curt,
Welcome to the Ask an Expert forum.
I can think of a few possibilities. Is your aluminum foil ball too far from the edge of the pie pan? Is the static electricity in your styrofoam plate being discharged before you set the pie plate on top of it? what happens if you hold the styrofoam plate near the foil ball? Does the ball move?
Please let us know how it goes.
Chris

[agm]

Hi Curt,

It's very helpful that you checked to see whether the ball would react to the balloon -- because of conservation of charge, we know that if the balloon acquired some charge, the styrofoam plate that you rubbed it against must have acquired the opposite charge.

However, a likely explanation is that the styrofoam somehow lost the charge before it came into contact with the aluminum pie plate. Charge will tend to flow through things that are grounded. The Earth is such a huge reservoir that the same number of electrons that would significantly affect something like a balloon or a plate or even a person can distribute themselves much more widely over its surface, and that situation is energetically preferable.

Anyway -- if you are doing this on top of an all-metal table, for example, the above is almost certainly what's happening. To make sure that the charge stays on the styrofoam plate, you could stand on a plastic stool and use a plastic table (wood would probably be fine, too). As long as *you* aren't grounded, you should be able to touch everything without a problem.

As Chris suggests above, it's also possible that the metal ball is not moving freely enough to respond to the charge -- but it sounds like it moved freely toward the balloon? Can it move back toward the plate as easily?

Good luck, and let us know how it works out!

Amanda

[Curt Searcy]

Chris and Amanda,

thank you both very much for your responses. I have been performing the experiment on a laminate counter top, so no metal involved there. The ball does seem to flow freely towards the balloon, and at times in the experiment, when I'd use the tip of my finger and move it towards the ball, the ball seemed to be repelled. Thus, I know something is being charged. I will try your suggestions and let ya know how it works. One other thing. In doing some research, I saw that humidity levels can affect the outcome. I live in central Florida, and it is moderately humid right now. Perhaps that is affecting the ball's reaction.

[Craig_Bridge]

I live in central Florida, and it is moderately humid right now. Perhaps that is affecting the ball's reaction.

Humid air will affect how long the charge stays static (in place) in this experiment.

I have been performing the experiment on a laminate counter top

My recommendation would be to use a clean clear dry glass tumbler to hold the metal pie plate off the counter top. If you have access to clear Mason / Ball quart or pint canning jars, they are great insulators. You can place 4 of them on the floor to support a piece of plywood to stand on and use one on the counter to hold the electroscope.

The problem with most plastics is the pigments used to color them are not good insulators and many of the coatings used on their surface are designed to be somewhat conductive to reduce static buildup.

The problem with wood is that it absorbs moisture and becomes somewhat conductive.

When you are dealing with moving moist air all these little leakage paths add up and reduce the effects and the time that the effects are observable.