Electric Fields

1
Electric Fields

• Sections 22.1-22.14

2
Review of Eclectic Charge
3
Review Electric Charge

• Let two charged particles (point charges) have
  charges q1 and q2 and be separated by a distance
  r.
• What is the electrostatic force of attraction or
  repulsion between them?

r
q2
q1
4
Review Electric Charge

• Coulombs Law
• Each particle exerts a force of this magnitude on
  the other particle.

5
Review Electric Charge

• Coulombs Law
• Do the particles repel each other or are they
  attracted to each other?

6
Review Electric Charge

• Opposite signs attract each other.
• Like signs repel each other.
• "The laws of gravity cannot be held responsible
  for people falling in love."
• Albert Einstein

7
Electric Fields

• How can one particle know about another
  particle in such a way as to act on it?
• We can answer those questions by saying that one
  particle sets up an electric field in the space
  surrounding it.

8
Electric Fields

• Electric Fields are vectors fields that consist
  of a distribution of vectors.
• Note Vectors have both __________ and
  ___________!

9
Electric Field Definition
Point P
r

qo
Test charge
q0 Positive charge
10
Electric Field Lines (Direction) for a Single
Point Charge

• Electric field lines for a single positive
  particle.

11
Electric Field (Magnitude)for a Single Point
Charge

• The magnitude of the vector E tells you how many
  Newtons per Coulomb a positive charge will
  experience when placed a Point P.

12
Electric Fields for multiple charges
Point P
r1

qo
r2
Test Charge 1
-
Test Charge 2
13
Electric Field Lines (Direction) for a Two
Opposite Point Charges
Note The direction of the electric field is
tangent to the field lines.
14
Field Lines

• Field lines trace the direction of the Electric
  field through space
• Field lines extend from positive to negative
• The direction of the electric field is tangent to
  the field lines.
• Field lines represent the direction the net force
  of the charge (q0) will be acting.

15
Electric Field Lines (Direction) for a Two Equal
Positive Point Charges
16
Electric Field Lines (Direction) for a Two
Oppositely Charged Plates
17
Electric Fields for multiple charges
Point P
r1

qo
r2
Test Charge 1
-
Test Charge 2
18
Superposition

• For any charge distribution the Electric Field
  (vector) is just the sum of the individual
  charges from all the charges in the distribution.

19
Electric Fields for multiple charges
r1

qo
Point P
r2
Test Charge 1
-
Test Charge 2
20
Examples