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Electric Fields
Electric fields are said to exist in the space
around CHARGED objects.
Electric Field Maps
Electric field lines around a charged object can
be mapped by imagining the direction that
a POSITIVE test charge would move
in that region of space
1. Place the test charge near the object
2. Decide which direction the charge will move
3. Draw a field vector in the direction of motion
Area around a
POSITIVE charge
+
Field lines point:
OUTWARD from +
INWARD toward -
+
Area around a
NEGATIVE charge
-
+
Electric Field Mapping
Field lines NEVER CROSS
+
+
-
Electric Field Mapping
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+
Electric Field
Electric fields are said to exist in the area
near CHARGED objects.
A strength of the electric field E
experiences ELECTRIC FORCE
per unit charge placed in that field:
E= F /q
Example
• 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= F/q
E = -300 N / -2 C
E = 150 N/C
Unit for electric field
strength is
Newton per Coulomb
Example
The amount of force depends on:
-Strength of the field (E)
-Charge on the object (q)
F= Eq
• 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?
F=Eq
F = (3 x 103 N/C)(0.03 C)
= 90 N