Transcript electric field - Broadneck High School

Describe how a negatively charged balloon
would interact with:
-another negatively charged balloon
-your positively charged hand
-two positively charged hands on
either side, equal distance apart
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Outcome:
The student will be able to identify
and calculate properties of
electric fields through written
practice and student led
instruction.
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What will we actually be doing?
Drill
 Outcome
 Review
 Quiz
 Power point
 Classwork

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Electric Fields
Chapter 21.1: Creating and
Measuring Electric Fields
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Remember the Balloon Lab?
How did the balloons react?
 Did it work in three dimensions?
 What else creates forces in 3
dimensions?

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Relationship to gravity
Much like gravity, electric force is
inversely proportional to the distance
squared
 Fg = GM1M2/d2
 F = Kq1q2/d2

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How can a force be
exerted across what seems to be
empty space?
WHAT???

Michael Faraday suggested that
because an electrically charged object,
A, creates a force on another charged
object, B, anywhere in space, object A
must somehow change the properties of
space. Object B somehow senses the
change in space and experiences a
force due to the properties of the space
at its location. We call the changed
property of space an electric field.
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In simple terms:

An electric field means that the
interaction is not between two distant
objects, but between an object and the
field at its location.
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Electric Fields
Can do work, transferring energy
 This is shown when using appliances

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How do we calculate electric
fields?
Place a small charged object at some
location.
 If there is an electric force on it, then
there is an electric field at that point.
 q’ is the symbol for test charge

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F is in Newtons
q is in Coulombs
What is E going to be in?
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Test Charge
Smaller test charge (q’) = what force?
 Larger test charge magnitude = what
force?
 Does electric field magnitude change
with different test charge size?
 What happens if you use too large a test
charge?

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All are vector quantities
 For charge use + or  Mr. Schwenke and Mr. Witmer
recommend using words for direction
not + or 
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Drawing electric Fields
Positive charges push things away
 Negative charges pull things towards
 Field lines should be in proportion to
charge

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Creating electric fields

http://www.cco.caltech.edu/~phys1/java/
phys1/EField/EField.html
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Exit ticket

Take out a piece of paper and draw an
electric field between a +1 charge and a
-2 charge
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