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PHYSICAL SCIENCE
Electricity
Part 1: Electric Charge and Force
13.1 Electrical Charge and
Force Objectives
Indicate which pairs of charges will
repel and which will attract.
Explain what factors affect the strength
of the electric force.
Describe the characteristics of the
electric field due to a charge.
Electric Charge
Electric charge is an electrical property of
matter that creates a force between objects.
There are two types of charges, opposite and
negative.
Opposite charges are attracted, like charges
repel one another.
There is no net charge when there is an
equal amount of positive and negative
charges.
Electric Charge
Electric Charge
Whenever there is an imbalance in the
number of protons and electrons in an
atom, molecule or other object, it has a
net electric charge.
Objects with a negative charge have
more electrons than protons.
Positively charged objects have fewer
electrons than protons.
Electric Charge
The SI unit of electric charge is the coulomb
(C).
An electron and a proton have exactly the
same measure of charge, 1.6 x 10-19 C, -1.6 x
10-19 C for an electron, and +1.6 x 10-19 C for
a proton.
For example, an object with a total charge of
–1.0 C has 6.25 x 1018 excess electrons.
Conductors and Insulators
A conductor is a material that transfers
charge easily.
An insulator is a material that does not
transfer charge easily.
An electrical cord has a conductor which
transfers electrical charges which is
surrounded by an insulator like plastic which
keeps the charge from taking an unintended
path.
Transfer of Electrons
Electrons can easily be transferred from one
object to another as objects are rubbed
together.
The direction in which the electrons are
transferred depends on the material.
Charging by friction is when two materials are
rubbed together; one loses electrons and
becomes positively charged, the other gains
electrons and becomes negatively charged.
Transfer of Electrons
Touching a charged object to a neutral
object in order to produce a net charge
in the neutral object is called contact.
The charges in a neutral object can be
redistributed without changing the net
charge of the object when a charge has
been induced and the charges are
realigned.
Electric Force
Electric force is the force of attraction or
repulsion between objects due to charge.
The electric force between two charged
objects varies depending on the amount of
charge on each object and the distance
between them.
The electric force is inversely proportional to
the square of the distance between two
objects.
Electric Field
Electric force does not require that objects
touch.
An electric field is the region around a
charged object in which other charged
objects experience an electric force.
Electric field lines point in the direction of the
electric force on a positive charge.
Electric field lines never cross.
Electric Field
Electric Field
Field lines show the direction of the
electric field as well as the relative
strength due to a given charge.
More lines are drawn for greater
charges to indicate greater force.