Electric Fields

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Electric Fields
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What is an electric field???

• It is an area of influence around a charged
  object.
• Positively charged objects within that field
  will experience an electrical force.

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Test Charge
Electric Field
Electric Field
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Calculating the magnitude of an electric field

• The magnitude is proportional to the amount of
  electrical force exerted on the positively
  charged object.
• Electric Field Strength electric force/test
  charge
• E Felectric/q0
• SI Unit N/C

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Sample Problem
Mr. Luna pulls a wool sweater over his head,
which charges his body as the sweater rubs
against his cotton shirt. What is the electric
field strength at a location where a 1.60 x 10-19
C piece of lint experiences a force of 3.2 x 10-9
N as it floats near Mr. Luna?
q0 1.60 x 10-19 C
F 3.2 x 10-9 N
E Felectric/q0
3.2 x 10-9 N / 1.60 x 10-19 C
E 2.0 x 1010 N/C
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Calculating the strength of an electric field

• The strength of an electric field depends on
• 1. the charge produced by the electric
  field
• 2. the distance between the test charge and
  the
• electric field
• Electric Field Strength Coulomb constant x
  field charge/ (distance)²
• E (Kc x q)/r²
• Kc 8.99 x 10 9 N m² / C²

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Sample Problem
A fly accumulates 3.0 x 10-10 C of positive
charge as it flies through the air. What is the
magnitude and direction of the electric field at
a location of 2.0 cm away from the fly?
q 3.0 x 10-10 C
r 0.02 m
Kc 8.99 x 109 N m² / C²
E (Kc x q)/r²
(8.99 x 109 Nm²/C²) (3.0 x 10-10 C)
(0.02 m)²
E 6743 N/C away from the fly
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Electric Field Lines

• Represent the magnitude and direction of an
  electric field with respect to the positive test
  charge.

More arrows greater magnitude
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Electric Field Lines

• When two point charges of equal magnitude, but
  opposite signs interact with each other, they
  form an electric dipole.

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Electric Field Lines

• Like charged objects that interact with each
  another, have their field lines moving away from
  one another.

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Electric Field Lines

• When interacting charges are of a different
  magnitude, only a fraction of the field lines
  from the greater charge will move to the lesser
  charge.