Electric Force The Electric Field

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Electric ForceThe Electric Field

• PHYS 2326-3

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Electric Field

• Forces work between specific objects
• An electric field is what that force would be for
  a test object with a unit charge
• F qE
• where F is the force acting on an object
• q is the charge of that object
• E is the electric field at the location of that
  object

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Point Charge Electric Field

• Force between 2 point charges

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Electric Field Lines

• Begin on positive charges
• End on negative charges
• Lines cannot cross
• Points in the direction of the electric field
  vectors
• Electric field vector tangent to electric field
  line at each point
• Density of lines indicate field strength

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Electric Dipole

• Not in this chapter see 26-6
• Consists of q, q charge, separation 2a
• Dipole moment magnitude p 2aq
• Vector goes from charge to charge
• Uniform electric field E
• Forces on charges equal and opposite directions

Net force on dipole 0 There is a net torque t
2Fa sin ? t pE sin ? Vector cross product
Potential energy of this dipole is

P
?
2d
-
Field E
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Electric Dipole Example 1

• Given q1.0E-8 C, d2.0m, k9E9 Nm2/C2
• where q is at x-1.0m, q is at x 1.0m
• What is E at (a) x0, (b) x2, (c) x0, y1, (d)
  the dipole moment ?

(c)
1m
(b)
(a)
-

1m
1m
1m
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Example 1(a)
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Example 1(b)
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Example 1(c)
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Example 1(d)