1. Mechanisms for Transfer of Charge
Restless Electrons
Mechanisms for Transfer of Charge

2. How do objects gain “static” charge?
Friction
Rubbing two electrically neutral objects together can charge both objects – both gain OPPOSITE charge
Conduction
Charged object TOUCHES another object – electrons jump from one to the other in an attempt to EQUALIZE the charge on both objects
Induction
Charged object comes near another object WITHOUT TOUCHING – causes it to POLARIZE

3. Conductive Properties of Solids
metal alloys
special
metals
silicon
wood
rubber
sea water
pure water
SUPER CONDUCTORS SEMI INSULATORS
CONDUCTORS CONDUCTORS
Conductors
allow charge to
flow through them
easily
high conductivity
Insulators
inhibit charge
flow
high resistivity

4. This works best when two INSULATORS are rubbed
Friction
This works best when two INSULATORS are rubbed
against one another

5. Conduction Negative To Neutral- -
Excess electrons exert repulsive forces
on one another, causing them to
move apart as much as possible
BOTH now have the same charge!

6. Conduction Positive To Neutral+ +
Electrons in the neutral object experience
an attractive force. They neutralize some of the
positive charge, leaving both with a lack of
electrons
BOTH now have the same charge!

7. Induction Negative To Neutral-
Polarization + -
Excess electrons exert force
against nearby electrons in the
neutral object

8. Induction Positive To Neutral+
Polarization - +
Electrons in the neutral object experience
an attractive force, which pulls them
closer to the charged object

9. Grounding In either case, grounding a charged object makes it neutral
Since the Earth is so large it
can equalize
charges from other
objects very easily
The Earth can equalize
charge by:
absorbing
excess electrons from
negatively charged objects
giving free
electrons to positively
charged objects
In either case, grounding a charged
object makes it neutral
One symbol that is often used to show that
something is grounded is:

10. - - - - - - - Electroscope An electroscope is a device that
detects CHARGE - - - - -
When the scope is CHARGED, the
LEAVES at the bottom will REPEL one another
The charged LEAVES
exert force on one
another, forcing
them apart - -

11. Electroscope – negative cond.
Step 5
Scope is once again
neutral – excess electrons
are gone
Step 3
Scope is now negatively
charged
Step 4
Scope is grounded
allowing electrons to
escape
Step 1
Negative rod touches
neutral scope
Step 2
Electrons spread out
and charge plates - - - - - - -

12. Electroscope – positive cond.
Step 4
Scope is grounded –
electrons from the ground
are attracted to the positive
scope
Step 5
Scope is once again
neutral – balanced charge
is restored
Step 2
Electrons leave scope
because they are attracted
to the positive rod
Step 3
Scope is now positively
charged
Step 1
Positive rod touches
neutral scope + - + - - - - + - +

13. Electroscope – negative ind.
Step 3
Rod is removed – electrons
are attracted back to the top
and “re-neutralize” the
electroscope.
Step 2
Scope polarizes as electrons
at the top try to move away
from the charged rod.
Step 1
Negative rod brought near
grounded scope - - + -

14. Electroscope – positive induction
Step 3
Rod is removed. Electrons
are attracted back into the
leaves by the protons,
making the electroscope
neutral again.
Step 2
Electrons from the bottom
of the electroscope are
attracted to the
positive rod – get pulled up.
The leaves get a positive
charge on them.
Step 1
Positive rod is brought near
neutral electroscope + - + - +

15. Electroscope – ind. with ground
Step 3
Ground is removed while the
rod is still nearby, keeping
electrons from re-entering
the scope
Step 5
The rod is taken away and the
positive charge remains
on the scope
Step 4
Scope now has a charge that
is opposite to the charge on
the rod
Step 2
Excess electrons from the
rod force electrons from the
scope into the ground.
Step 1
Negative rod brought near
grounded scope - + - - + - +

16. Electroscope – ind. with ground
Step 3
Ground is removed, while the
rod is still nearby, pulling on
electrons and keeping them
from escaping
Step 4
Scope is now negatively
charged – the opposite
charge as that of the
rod
Step 5
Rod is taken away and
the negative charge remains
on the scope
Step 1
Positive rod is brought near
grounded scope
Step 2
Electrons from the ground
are attracted to the
positive rod + - - -