Download Electric Fields

Topic 6.2
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What are the two types of
charges?
How do neutral object interact
with charged objects?
What is the difference between
insulators and conductors?
Can there be electricity in
insulators?
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What causes the movements?
Describe the movements in
terms of “action at a distance”
How do you know there’s a
force if it’s not touching?
What’s happening to the
charges in each interaction?
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What are the variables that affect the electric
force on an object?
It was found that
qq
1q
1q
F
 k ( 2 22 2 )
rr
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Charles-Augustin de Coulomb
Describe a method in finding
the constant
(1736 –1806)
that will make this proportion into an
equation
The constant k is sometimes
written as
k = 1/4πεo
where εo is called the
permittivity of free space.
What is the value & unit for k?
The force between two charges is 20.0 N. If
one charge is doubled, the other charge
tripled, and the distance between them is
halved, what is the resultant force between
them?
F = 20N
q1
q2
r
2q1
F = ?480
N N
r/2
3q2
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Is it possible to have a force with only one
object?
What causes you to know there’s a force on
you (or any object) if it’s not touch you?
How do we know our description of forces
(and fields) are correct?
Can we ‘see’ field lines?
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An area or region where a charge feels a force
is called an electric field.
The electric field strength at any point in
space is defined as the force per unit charge
(on a small positive test charge) at that point.
What is the unit of an electric field?
 E = F/Q (in N.C-1)
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Is the electric field a vector or scalar?
Describe the concept of field lines in one
sentence
What would the field lines look like for a
single charge?
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An electric field can be represented by lines
and arrows on a diagram, in a similar ways to
magnetic field lines.
What about
the direction?
Defined to be a positive charge that is small
enough so it does not have an effect on the
field
Defined to be a positive charge that is small
enough so it does not have an effect on the
field
The arrows
show the
direction of
force that
would be felt
by a positive
charge in the
field
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In what direction will the test charge feel the
force from the negative charge?
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In what direction will the test charge feel the
force from the negative charge?
The arrows
show the
direction of
force that
would be felt
by a positive
charge in the
field
Electric field is a vector, and any calculations
regarding fields (especially involving adding
the fields from more than one charge) must
use vector addition.
Field here due to
both charges?
q1
q2
Electric field is a vector, and any calculations
regarding fields (especially involving adding
the fields from more than one charge) must
use vector addition.
Field due to q1
Field here due to
both charges?
q1
q2
Electric field is a vector, and any calculations
regarding fields (especially involving adding
the fields from more than one charge) must
use vector addition.
Field due to q2
q1
Field due to q1
Field here due to
both charges?
q2
Electric field is a vector, and any calculations
regarding fields (especially involving adding
the fields from more than one charge) must
use vector addition.
Field due to q2
Field due to q1
Resultant field
q1
q2
Sketch what you think the field lines should
look like:
Sketch what you think the field lines should
look like:
V
d
d
“Edge effects”
Uniform field E =
V/d
V