Charging by Electrostatic Induction

When an object gets charged by induction, a charge is created by the influence of a charged object but not by contact with a charged object.  The word induction means to influence without contact.  In the example shown below, the electroscope gets charged without any contact with the charged object brought in from the top. 

1. The  charged object is brought near the neutral electroscope.   This causes many electrons to move toward the top to be near the positive charge.
2. While the charged object is still near (but not touching) a connection to ground (via your finger)  is created to the electroscope.  In this case, some electrons from your finger are drawn into the electroscope by the charged object.   The electroscope now has an excess of electrons, (but often the leaves go flat because the majority of them are at the top, the bottom is neutral. - not shown in this animation)
3. The attachment to ground is removed (you take away your finger).   This strands the electrons on the electroscope so it now has  negative charge.  
4. Pull the charged object away, the leaves move apart.  It is charged!

There are several advantages to charging something by induction.

• The originally charged object never loses any charge so it need not be recharged.  (work does not need to be done creating the charge again)
• The induced charge can be quite strong and subsequent charges will be equally strong

The table below compares charging by Conduction to charging by Induction.

©1999 Science Joy Wagon