Download Electric Fields Field Theory: A force is a push or a pull. A field is a

Electric Fields
Field Theory: A force is a push or a pull. A field is a region where an object may experience a force. The
field has a source, which is an object which exerts the force. A force can be gravitational, electric, or
magnetic in nature. Fields of force have direction and magnitude (an amount of strength) and so we can
call them vector fields and represent them mathematically using vectors.
Forces can be represented
using field lines. The field
lines indicate the direction of
the force. The force is more
intense where the field lines
are the most dense. Field
lines may not cross. Fields of
force can interact with each
other.
Electric forces can be attractive or repulsive. Like charges repel each other with an electric force of
repulsion. Unlike charges similarly attract each other with a force. The attractive force between unlike
charges acts just like the gravitational force between two masses.
Two objects with unlike charge attract each other. Two objects with like charges repel each other.
Electrons orbit the nucleus of an atom. Some
electrons are loosely held and can be transferred
from one object to another.
The amount of charge on an object is the number
of electrons in excess or deficit. It is a comparison
of the numbers of electrons and protons.
Electrons can be transferred from one object to another by friction.
The electric force exerted by one object on another depends on the charges on the two objects and how
far apart they are.
FE =
Compare the concepts of gravitational force and electric force using the Venn diagram below.
Turn text to visual to explore and develop your understanding and interpretation of the reading..
The electric potential at a certain location in a
field is V and is the amount of electric energy
per unit charge q.
V
∆E
q
Pulling your wool sweater off makes your hair stick up because of the static charge that develops.
Friction between the wool and your hair causes electrons to move to the material with the higher
attraction for them. Why does pulling off your sweater
cause a spark to jump from the sweater back to the
person?
The following selection from your text explains how lightning is produced.
Think back to the last time you saw a sky like this. Can you remember what the weather was like that
day?
At first, this may seem like a ridiculous question, but it is not coincidence that most thunderstorms
occur late in the afternoon or evening of a very hot, humid summer day. The reason for this is that it
takes the intense summer sun to make the
air hot and rich in water vapour. Warm air
floats up in cooler surrounding air—like a
cork in water. As it rises, the water vapour
starts to condense and forms a cloud. The
condensation releases energy, which
causes the air parcel to get even warmer
and rise even higher.
Sometimes the top of a thundercloud can
reach 12–20 km above the ground! As a
column of warm water vapour rushes up, it
comes in contact with a column of
condensed water droplets that are
descending. Since the water droplets more
readily hold on to their electrons than the
rising water vapour does, electrons are
transferred from the rising water vapour to
the descending water droplets. The result
is that the bottom of the cloud has an
excess of electrons, so it is negatively charged. The top of the cloud has lost electrons, so it is positively
charged.
Recall from previous courses that objects with opposite charges attract each other, while objects that
have the same type of charge repel one another
A lightning strike transferred about 15 C of charge from a cloud to a building. The voltage between the
cloud and the building was 1.50x108 V.
a) Calculate the energy delivered in the lightning
strike
b) A typical home in Alberta uses 3.0 x 109 J of
electrical energy every month. Comparethis
amount to the amount of energy in the
lightning strike.
Read about fields and field lines in your text unit C 1.1 p.312-327.