Bell Ringer Field and Force
Between the red and the
blue charge, which of
them experiences the
greater electric field due
to the green charge?
+1
d
+2
1)
+1
2)
+2
3) the same for both
+1
d
+1
Bell Ringer Field and Force I
Between the red and the
blue charge, which of
them experiences the
greater electric field due
to the green charge?
+1
d
1)
+1
2)
+2
3) the same for both
+2
Both charges feel the same electric
field due to the green charge because
they are at the same point in space!
+1
d
+1
Q
Ek 2
r
Electric Charge and Electric Field
Electric Field Lines
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Electric Field Lines
• Since the electric field is a vector, it is sometimes
referred to as a vector field
• The electric field can be represented by field lines.
These lines start on a positive charge and end on a
negative charge.
© 2014 Pearson Education, Inc.
Electric Field Lines
• The number of field lines starting (ending) on a
positive (negative) charge is proportional to the
magnitude of the charge.
• The electric field is stronger where the field lines are
closer together.
• The direction of the electric field at any point is
tangent to the field line at that point.
Electric dipole: two equal
charges, opposite in sign:
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Electric Field Lines
Electric field lines for two
equal positive charges
• Unequal charges –Q, and +2Q.
• Note that twice as many lines
leave +2Q as enter –Q (number
of lines is proportional to
magnitude of Q).
© 2014 Pearson Education, Inc.
Electric Field Lines
The electric field between two
closely spaced, oppositely charged
parallel plates is constant.
© 2014 Pearson Education, Inc.
Electric Field Lines
Summary of field lines:
1. Field lines indicate the direction of the field;
the field is tangent to the line.
2. The magnitude of the field is proportional to
the density of the lines.
3. Field lines start on positive charges and end
on negative charges; the number is
proportional to the magnitude of the charge.
© 2014 Pearson Education, Inc.