Physics Unit 8
Electricity and Magnetism
2 Forms of Electricity
1. Static – a build up of charge on an object
2. Current – a steady flow of electric charge
through a conductor
Static Electricity
• When objects are rubbed together, electrons
can transfer from one object to another.
 the object that loses electrons takes on a
positive charge.
 the object that gains electrons takes on a
negative charge.
Static Electricity
Balloon is neutral.
(Same # of Protons as
Electrons)
Hair is neutral.
(Same # of Protons as
Electrons)
+
-
+
+
+
+
Static Electricity
When rubbed together,
the balloon accepts
electrons from the
hair.
When rubbed together,
the hair donates
electrons to the
balloon.
Static Electricity
Balloon becomes
negatively charged.
Hair becomes positively
charged.
_
+
-
-
-
-
_ +
e-
+
_
+
+
-
+
Static Electricity
• Opposite charges attract. The hair is
attracted to the balloon.
-
-
-
-
-
Static Electricity
• Each hair takes on a positive charge. Hairs
stand apart from each other because similar
charges repel each other.
Law of Attraction and Repulsion
• Opposite charges attract.
• Similar charges repel.
Static Electricity
• If you scuff your feet on the carpet, electrons leave
the carpet and are stored in your body.
• As long as you remain insulated from other
objects, you simply walk around with excess
negative charges. You have Potential Difference
(Voltage)!
• When you touch another conductor, the charge
transfers to that object. You feel a static electric
shock.
In addition to Friction, rubbing,
objects can also acquire a static
charge by:
• Induction: When
• Conduction:
an object with a
When two
charge comes close
objects make
to another object, it
contact, electrons
causes a temporary
transfer between
separation of
the two until their
charge in that
charges are
object.
equal.
Conduction
A negative wand comes
near a neutral sphere.
_
When they touch,
electrons travel from the
wand to the sphere.
_
_
_
Neutral
The sphere becomes (-)
charged by conduction.
Induction
A negative wand comes
near a neutral sphere.
_
_
+
+
_
_
The negative charge
in the wand repels the
electrons in the sphere.
The side of the sphere
near the wand becomes
+ charged by induction.
When the wand is
removed, the charge in
the sphere is removed.
Static Electricity
• An excess of electrons, static electric
charge, can be grounded by providing a path
of conductors to the earth.
Ex. Lightning rods on homes, grounding
plugs on electrical cords
Conductors and Insulators
Conductors:
Allow a free flow of
electrons.
Ex. Metals
(the wire inside an
electrical cord)
Insulators:
Slow or stop the flow
of electrons.
Ex. Rubber, Glass,
Plastic
(the rubber coating on
the outside of an
electrical cord)