Gold leaf electroscope important images - Class 12 PDF Download

 Page 1


 1 
The gold leaf electroscope  
 
 
This is an instrument for detecting and measuring static electricity or voltage. 
A metal disc is connected to a narrow metal plate and a thin piece of gold leaf is fixed to the 
plate. The whole of this part of the electroscope is insulated from the body of the instrument. 
A glass front prevents air draughts but allows you to watch the behaviour of the leaf. 
 
 
 
When a charge is put on the disc at the top it spreads down to the plate and leaf. This means 
that both the leaf and plate will have the same charge. Similar charges repel each other and 
so the leaf rises away from the plate - the bigger the charge the more the leaf rises. 
 
The leaf can be made to fall again by touching the disc - you have earthed the electroscope. 
An earth terminal prevents the case from becoming live. The electroscope can be charged in 
two ways: 
 
(a) by contact - a charged rod is touched on the surface of the disc and some of the charge 
is transferred to the electroscope. This is not a very effective method of charging the 
electroscope. 
 
(b) by induction - a charged rod is brought up to the disc and then the electroscope is 
earthed, the rod is then removed. 
 
The two methods give the gold leaf opposite charges. 
 
The diagrams on the following page show you how the charges spread over the plate and 
gold leaf in different conditions. 
 
 
 
 
 
Metal stem 
Metal plate 
Earth connection 
Glass window 
Metal disc 
Insulation 
Gold leaf 
Page 2


 1 
The gold leaf electroscope  
 
 
This is an instrument for detecting and measuring static electricity or voltage. 
A metal disc is connected to a narrow metal plate and a thin piece of gold leaf is fixed to the 
plate. The whole of this part of the electroscope is insulated from the body of the instrument. 
A glass front prevents air draughts but allows you to watch the behaviour of the leaf. 
 
 
 
When a charge is put on the disc at the top it spreads down to the plate and leaf. This means 
that both the leaf and plate will have the same charge. Similar charges repel each other and 
so the leaf rises away from the plate - the bigger the charge the more the leaf rises. 
 
The leaf can be made to fall again by touching the disc - you have earthed the electroscope. 
An earth terminal prevents the case from becoming live. The electroscope can be charged in 
two ways: 
 
(a) by contact - a charged rod is touched on the surface of the disc and some of the charge 
is transferred to the electroscope. This is not a very effective method of charging the 
electroscope. 
 
(b) by induction - a charged rod is brought up to the disc and then the electroscope is 
earthed, the rod is then removed. 
 
The two methods give the gold leaf opposite charges. 
 
The diagrams on the following page show you how the charges spread over the plate and 
gold leaf in different conditions. 
 
 
 
 
 
Metal stem 
Metal plate 
Earth connection 
Glass window 
Metal disc 
Insulation 
Gold leaf 
 2 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Charging by contact 
Charging by induction 
Earthed