Download Electric Fields - Xavier High School

Electric Fields
The electric field is a vector quantity that
relates the force exerted on a test charge
to the size of the test charge.
Huh?
Electric Fields
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What does Coulomb’s law tell us?
If an object is charged but nothing is close
enough to feel it…does the charge go away?
Why is the size of the test charge
important?
E= Fon q’
q’
Unit = ?
Let’s practice!
An electric field is to be measured using a
positive test charge of 4.0 x 10-5 C. This test
charge experiences a force of 0.60N acting
at and angle of 10°. What is the magnitude
and direction of the electric field at the
location of the test charge?
Answer: 1.5 X 104 N/C at 10°
Picturing the Electric Field
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Electric field lines show direction and strength of
the electric field.
Will positive and negative field lines be the
same?
Lines start on a positive charge and terminate
on a negative charge
The closer together the lines are, the stronger
the field
-Lines of force are
drawn perpendicularly
away from the
positively-charged
object and
perpendicularly into the
negatively-charged
object.
-Electric field lines
between the oppositely
charged objects are
bent…what dictates
this shape?
http://www.youtube.com/watch?v=gU0MUUVYyAU
Review
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A positive test charge of 5.0 X 10-4C is in an electric
field that exerts a force of 2.5 x 10-4N on it. What is
the magnitude of the electric field at the location of
the test charge?
Suppose the electric field in the problem above is
caused by a point charge. The test charge is moved
to a distance twice as far from the charge. What is
the magnitude of the force that the field exerts on
the test charge now?
You are probing the field of a charge of unknown
magnitude and sign. You first map the field with a
1.0 x 10-6 C test charge, then you repeat your work
with a 2.0 x 10-6 C test charge.
a) Would you measure the same forces with the two test
charges? Explain.
b) Would you find the same fields? Explain.