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Question Perin Tube - sign of electron charge

7 months 6 days ago - 7 months 6 days ago #41669 by RuthH
we have set the Perin tube up and are measuring the output with a coulombmeter. However as soon as we turn the power on the meter starts recording a charge which continues to increase regardless of where the beam is, deflecting the beam into the faraday cylinder has no effect on the recorded output. Is there something obvious which we may be doing wrong.

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7 months 5 days ago #41671 by D.B.Ferguson
My first thoughts are that there may be an issue with the coulomb meter. If you are using one of the small (same form as the suppliers ammeter/voltmeters), I have found these do drift without lots of precautions being taken.
This is commonly used on the "spooning charge" demonstration using Aluminium capacitor plates and a target plate.
I have an old KFD(?) electrometer/coulomb meter that isn't so prone to drift. This is a mains powered meter with lots of shielding.

I'll try and get back to you when I have had a chance to check my notes.

Technicians: providing solutions and more.

David Ferguson B.Sc.

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7 months 4 days ago #41673 by D.B.Ferguson
Just got back to reading my notes:
Obviously had an issue with this in the past. "Use a gold leaf electroscope to compare the charge to a known test charge".
E.g. use a second electroscope and charge using an EHT source. Then bring the charge on that plate to the Perrin tube charged plate using an electrophorus plate (a metal disc on an insulating rod)

Technicians: providing solutions and more.

David Ferguson B.Sc.
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