Science Fair Van de Graaff Generator

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• I am new to the group, and this is my first post. My son and I are building a Van de Graaff Generator for his 7th fair science fair. We are going to attempt
Message 1 of 4 , May 3 8:40 AM

I am new to the group, and this is my first post.

My son and I are building a Van de Graaff Generator for his 7th fair science fair.  We are going to attempt to use it to measure humidity.  We are hoping to calibrate is with a hygrometer, so that we can use it directly to measure humidity directly; humidity being the independent variable and spark length being the dependent variable.

We are using a rubber band to carry the charge from a Teflon roller to a glass roller at the top, under an inverted aluminum soda can.  At 15% relative humidity, it will make a ½-inch spark.  All of the designs I’ve find have the top roller at the center of the dome.  Is this important.  The top roller in our design is about an inch below the mounting of the can.

Once we complete the generator, I will post a picture.

• Hi Steve Yes it is important since if the roller is not inside the can then the charge will only accumulate until there is equal charge on the roller and the
Message 2 of 4 , May 4 7:55 AM
Hi Steve

Yes it is important since if the roller is not inside the can then the charge will only accumulate until there is equal charge on the roller and the can (equal charges repel each other). If you put the top roller in the can then the charge on the outside of the can can accumulate in theory indefinitely (of course not so in real life due to many leakage points).

Sent: Tuesday, May 03, 2011 5:40 PM
Subject: [VanDeGraaffGenerator] Science Fair Van de Graaff Generator

I am new to the group, and this is my first post.

My son and I are building a Van de Graaff Generator for his 7th fair science fair.  We are going to attempt to use it to measure humidity.  We are hoping to calibrate is with a hygrometer, so that we can use it directly to measure humidity directly; humidity being the independent variable and spark length being the dependent variable.

We are using a rubber band to carry the charge from a Teflon roller to a glass roller at the top, under an inverted aluminum soda can.  At 15% relative humidity, it will make a ½-inch spark.  All of the designs I’ve find have the top roller at the center of the dome.  Is this important.  The top roller in our design is about an inch below the mounting of the can.

Once we complete the generator, I will post a picture.

• Steve: Elmer’s response – right on! Dick Linder _____ From: VanDeGraaffGenerator@yahoogroups.com [mailto:VanDeGraaffGenerator@yahoogroups.com] On Behalf Of
Message 3 of 4 , May 4 10:41 AM

Steve: Elmer’s response – right on!

Dick Linder

From: VanDeGraaffGenerator@yahoogroups.com [mailto: VanDeGraaffGenerator@yahoogroups.com ] On Behalf Of Elmer Wiersma
Sent: Wednesday, May 04, 2011 10:56 AM
To: VanDeGraaffGenerator@yahoogroups.com
Subject: Re: [VanDeGraaffGenerator] Science Fair Van de Graaff Generator

Hi Steve

Yes it is important since if the roller is not inside the can then the charge will only accumulate until there is equal charge on the roller and the can (equal charges repel each other). If you put the top roller in the can then the charge on the outside of the can can accumulate in theory indefinitely (of course not so in real life due to many leakage points).

From:

Sent: Tuesday, May 03, 2011 5:40 PM

Subject: [VanDeGraaffGenerator] Science Fair Van de Graaff Generator

I am new to the group, and this is my first post.

My son and I are building a Van de Graaff Generator for his 7th fair science fair.  We are going to attempt to use it to measure humidity.  We are hoping to calibrate is with a hygrometer, so that we can use it directly to measure humidity directly; humidity being the independent variable and spark length being the dependent variable.

We are using a rubber band to carry the charge from a Teflon roller to a glass roller at the top, under an inverted aluminum soda can.  At 15% relative humidity, it will make a ½-inch spark.  All of the designs I’ve find have the top roller at the center of the dome.  Is this important.  The top roller in our design is about an inch below the mounting of the can.

Once we complete the generator, I will post a picture.

• Thanks for the responses. Presently, we are using rubber bands, stranded wire, and a soda can, and we are generating enough voltage (40 kV, assuming 3 kV/mm)
Message 4 of 4 , May 4 11:57 AM

Thanks for the responses.  Presently, we are using rubber bands, stranded wire, and a soda can, and we are generating enough voltage (40 kV, assuming 3 kV/mm) to produce a ½-inch spark.  What kind of arc might we expect, if we reconfigured  the set-up to put the top roller inside the can?

Thanks,

Steve

From: VanDeGraaffGenerator@yahoogroups.com [mailto:VanDeGraaffGenerator@yahoogroups.com] On Behalf Of Richard Linder
Sent: Wednesday, May 04, 2011 12:42 PM
To: VanDeGraaffGenerator@yahoogroups.com
Subject: RE: [VanDeGraaffGenerator] Science Fair Van de Graaff Generator

Steve: Elmer’s response – right on!

Dick Linder

From: VanDeGraaffGenerator@yahoogroups.com [mailto:VanDeGraaffGenerator@yahoogroups.com] On Behalf Of Elmer Wiersma
Sent: Wednesday, May 04, 2011 10:56 AM
To: VanDeGraaffGenerator@yahoogroups.com
Subject: Re: [VanDeGraaffGenerator] Science Fair Van de Graaff Generator

Hi Steve

Yes it is important since if the roller is not inside the can then the charge will only accumulate until there is equal charge on the roller and the can (equal charges repel each other). If you put the top roller in the can then the charge on the outside of the can can accumulate in theory indefinitely (of course not so in real life due to many leakage points).

From:

Sent: Tuesday, May 03, 2011 5:40 PM

Subject: [VanDeGraaffGenerator] Science Fair Van de Graaff Generator

I am new to the group, and this is my first post.

My son and I are building a Van de Graaff Generator for his 7th fair science fair.  We are going to attempt to use it to measure humidity.  We are hoping to calibrate is with a hygrometer, so that we can use it directly to measure humidity directly; humidity being the independent variable and spark length being the dependent variable.

We are using a rubber band to carry the charge from a Teflon roller to a glass roller at the top, under an inverted aluminum soda can.  At 15% relative humidity, it will make a ½-inch spark.  All of the designs I’ve find have the top roller at the center of the dome.  Is this important.  The top roller in our design is about an inch below the mounting of the can.

Once we complete the generator, I will post a picture.

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