Charging By Friction
When two objects are rubbed together, the
molecules are close enough together that
the electrons from one substance can
move onto the other substance.
The substance that gains extra electrons
becomes negatively charged, while the
substance with fewer electrons becomes
positively charged.
The more rubbing, the more transfer, the
greater the charge.
The Electrostatic Series
As previously discussed, some objects
hold their electrons tighter than others.
The electrostatic series ranks objects by
how easily they let go of e- during
friction.
Substances that let go easily are on top
and become positively charged.
Substances on the bottom hold tight and
take on a negative charge.
The further the substances are apart, the
more charge that it produced.
+
Acetate
Glass
Wool
Fur or hair
Silk
Aluminium
Cotton
Paraffin wax
Plastic
Rubber
Gold
-
Example
When clothes are put in a dryer without
fabric softener, they rub against each other
and become charged.
Which item would take on which charge if:
a) Cotton socks are dried with a wool sweater?
-
+
b) A wool sock is dried with a silk shirt?
+
-
When you comb your hair with a plastic
comb, your hair becomes statically
charged.
What is the charge on your hair?
+
On the comb?
-
What could you use to make a comb that
would produce less charge?
Hair +
Comb -
Aluminium
Acetate
Charging By Contact
Electric charge can be transferred
between objects just by touching them
together.
Charging by conduction occurs when a
charged object touches a neutral object.
A few electrons move from one object to
the other (electrons try to move where
they are needed).
As a result, both objects end up with the
same charge.
Charging By Introduction
Neutral objects are attracted to charged
objects.
In fact, a charged object can induce a
charge in another object.
The neutral object never actually gains or
loses any electrons.
When the charged object is brought close,
the electrons move slightly in the
uncharged object.
So if a positive object in brought near, the
electrons are attracted and move closer.
If the charge is negative, the electrons are
repelled and move away.
Discharging An Object
If you connect an electrical device or
something with a charge to the earth or
the ground, then the extra charges get
transferred into the Earth.
Since the Earth is so large, it can accept a
lot of electrons without having much effect.
This is called grounding an object.