Transcript How do electrons know what to do? 4.1.4 Electric Fields Electric

Do you have a
Clue How
to do this?
• An electrostatic force F acts between two
objects with charges +q and +q when they
are distance R apart. If the distance
between the objects is halved, the
electrostatic force would become:
Objectives
• Now that we understand that electrons
and protons have “charge” associated with
them, we can understand the electrostatic
Force.
• What is an electrostatic Field?
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How do electrons know
what to do?
4.1.4 Electric Fields
Electric Field Maps
• Electric fields…
• exist near CHARGED OBJECTS
• mapped using a POSITIVE test charge
• 1 – place test charge
• 2 – draw arrow in direction pushed
• 3 – this is the field direction
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Electric Field Maps
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Electric Field Maps
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Electric Field Strength
• Field strength…
• Gets WEAKER with distance
• FORCE exerted per unit CHARGE
+
E
r
C
A>C>B
A
B
Example #1
• An object with a charge of -2 coulombs positioned
in a uniform electric field experiences a force of 300 newtons. What is the strength of the electric
field?
E= Fe/q
E = -300 N / -2 C
E = 150 N/C
Example #2
• What is the force experienced by a 0.05 coulomb
charge when it is placed in an electric field with a
strength of 3 x 103 newtons per coulomb?
Fe = Eq
F = (3 x 103 N/C)(0.05 C)
F = 150 N
Parallel Plates
• Field strength…
• Between plates
• E  Fe = SAME AT ALL POINTS
• Outside plates = ZERO
+ + + + + + + + + +
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Hollow Charged Spheres
• Field strength…
• Normal field pattern outside
• ZERO inside
E=0
End of 4.1.4 - PRACTICE