4.Main Content
experiments
Gold leaf electroscope
Class experiment
The gold leaf electroscope is an historic instrument whose leaves diverge when it is charged.
Apparatus and materials
For each student group:
- Cloth for rubbing
- Gold leaf electroscope
- Acetate rod or strip
- Polythene rod or strip
Safety
Read our standard health & safety guidance
Procedure
a Rub the polythene rod and then transfer the charge to the electroscope by wiping it along the plate on the top.
b Find the effect on the gold leaf when you bring up first a polythene rod, then an acetate rod that have been rubbed with a cloth.
Teaching notes
1 This is a simple introduction to the gold leaf electroscope. The leaf rises because it has the same charge as the stem of the electroscope and like charges repel.
2 Students should observe that charge can be transferred to the electroscope by touching the top plate. This produces an excess charge (positive or negative) on the plate, stem and leaf.
They may also observe that the gold leaf starts to diverge before the charged rod touches the plate – there is ‘action at a distance’. In this case the total charge on plate, stem and leaf has not changed. It has simply been re-distributed. The plate and the stem-leaf now have equal but opposite charges.
3 An electroscope can only indicate the presence and relative magnitude of charge. What it actually measures is the potential difference between the top plate and the earth.
Thank you to Erneste Cabral for suggesting that we should label the diagram.
This experiment was safety-tested in August 2006