Charging by Contact
1. You can charge a neutral object by
rubbing it with a different material
(friction).
2. Sometimes, you can charge an object
just by touching it with another object
and then separating the two objects
(conduction).
• Electrons from one object move onto the
other object.
11.2
Charging by Contact: Friction 11.2
neutral
What is the charge on the
hair?
What is the charge on the
comb?
neutral
Charging by Contact: Friction 11.2
After combing
positive
negative
What is the charge on the
hair?
What is the charge on the
comb?
Why do the comb and hair
attract?
They are oppositely charged.
How can we determine the
charge that develops on
each object?
Charging by Contact: Friction
The electrostatic series helps you determine
whether an object will become positively or
negatively charged when it is rubbed with a
different material.
– For two materials, look at their positions in
the electrostatic series.
– The material closer to the top of the list will
lose electrons and become positively
charged.
– The material near the bottom of the list will
gain electrons and become negatively
charged.
11.2
electrostatic series
Handout: Charging Objects by
FRICTION
This method of charging objects involves rubbing two
neutral objects together. The contact allows
electrons to be transferred from one substance to
___________
the other substance. One substance will gain
negatively
electrons (and become ______________
charged) while
the other will lose electrons (and become
positively
______________
charged). Since the two objects have
attract
opposite charges, they will ______________
each
other.
Handout: Charging Objects by
FRICTION
The various atoms that make up all substances have
different forces of attraction for electrons. Some have
a strong hold on electrons while others have a weak
hold on electrons. A list showing the relative attraction
of different substances for electrons is shown on the
next handout. This list is called the
Electrostatic Series
________________________________.
Handout: Charging Objects by
FRICTION
Example:A piece of fur is rubbed with an ebonite rod. What
is the charge on each object and explain how the charge
was produced?
If we look to the Electrostatic Series, we see that the
ebonite has a ______________
hold for electrons than fur.
stronger
When the fur and ebonite are rubbed together, some
electrons from the __________
move to the
fur
______________
because ebonite has the ______________
ebonite
stronger
attraction for electrons.
ebonite
Since the _____________
gains electrons, it becomes
________________
charged.
negatively
Since the _____________
loses electrons, it becomes
fur
________________
charged.
positively
Handout: Charging Objects by
FRICTION
Example:If cat fur is rubbed with a glass rod;
stronger
The fur (having a ________________
hold on electrons)
gain
will ____________
electrons and become
________________
charged.
negatively
weaker
The glass (having a _______________
hold on
lose
electrons) will ____________
electrons and become
positively
_______________
charged.
11.2
Charging by Contact: Conduction
A neutral object can become charged if you touch it with a charged
object.
• If the charged object is negatively charged, electrons will move
onto the neutral object.
• If the charged object is positively charged, electrons from the
neutral object will move onto the positively charged object.
The negatively charged rod is moved
toward a neutral pith ball electroscope so
that both objects touch
While the two objects are touching, some
electrons from the rod move onto the pith ball
Charging by Contact: Conduction
If two charged objects touch, electrons will move away from
the object with more electrons until both objects have the
same charge.
Handout: Charging Objects by
CONDUCTION
This method of charging objects involves contact between a
charged object and a neutral object.
Example #1: A negatively charged rod touches a neutral pith ball.
The _____________ on the negatively
charged rod repel each other and jump
from the _________ to the
________________. The negative rod
has shared its electrons with the pith
negative
neutral
ball and they are now both
________________ charged.
Handout: Charging Objects by
CONDUCTION
This method of charging objects involves contact between a
charged object and a neutral object.
Example #1: A negatively charged rod touches a neutral pith ball.
The _____________
electrons on the negatively
e-
charged rod repel each other and jump
rod
from the _________
to the
pith ball
________________.
The negative rod
has shared its electrons with the pith
negative
negative
neutral
ball and they are now both
________________
charged.
negatively
Handout: Charging Objects by
CONDUCTION
***
The neutral object gets the ___________
charge as
same
the charged object since the charged object shares
its charge with the neutral object.
Handout: Charging Objects by
CONDUCTION
Example #2: Show the charge distribution and the
position of the leaves of the metal-leaf electroscope
before and after being touched by a positively charged
rod.
Neutral
Positive
Before
After
Handout: Charging Objects by
CONDUCTION
Example #2: Show the charge distribution and the
position of the leaves of the metal-leaf electroscope
before and after being touched by a positively charged
rod.
Neutral
Positive
Before
After
Handout: Charging Objects by
CONDUCTION
When the positively charged object touches the neutral
electrons jump from the
electroscope, ______________
__________________
to the ___________
(because of
electroscope
rod
the attraction between electrons and protons). The
positively
electroscope is now ____________________
charged
lost
because it ___________
electrons. Since it is charged, its
repel / separate
leaves will __________________.
Handout: Charging by
CONDUCTION
Figure 1
ee-
Neg
Handout: Charging by
CONDUCTION
Figure 2
e-
e-
Handout: Charging by
CONDUCTION
Figure 2
e-
e-
Pos
Grounding
11.2
When a charged object touches a large neutral object
such as Earth, the charged object becomes grounded
and loses its net charge.
– If the charged object was positively charged, electrons
from the large neutral object move toward the charged
object.
– If the charged object was negatively charged, electrons
move away from the charged object toward the neutral
object.
Grounding
Step 1
Hand is negatively
charged.
Faucet is neutral.
11.2
Grounding
Step 2
When the hand is
close to the faucet,
some electrons from
the hand move
toward the faucet
and create an
electric discharge.
11.2
Grounding
Step 3
After grounding, the
hand loses
its negative charge.
The extra
electrons go into
Earth.
11.2
Symbol for Grounding
11.2
Electrostatic Dusters
Electrostatic Precipitators
Homework
p. 477 # 1-8