18.7 Electric Field Lines
An isolated point, positive charge:
18.7 Electric Field Lines
18.7 Electric Field Lines
18.7 Electric Field Lines
Electric field lines are always directed away from positive
charges.
Electric field of a negative
point charge
Electric field of a negative
point charge
The electric field lines are directed radially inward toward a
negative point charge.
Electric field between two
parallel plates
Electric field between two
parallel plates
Electric Dipole
An electric dipole consists of two separated point charges
that have the same magnitude but opposite signs.
Electric Dipole
An electric dipole consists of two separated point charges
that have the same magnitude but opposite signs.
Electric Dipole
An electric dipole consists of two separated point charges
that have the same magnitude but opposite signs.
The dipole moment, p is the product of the magnitude of
one of the charges and the distance between the charges.
p=qL
Electric Dipole
An electric dipole consists of two separated point charges
that have the same magnitude but opposite signs.
The dipole moment, p is the product of the magnitude of one of
the charges and the distance between the charges.
p=qL
Many molecules, such as H2O and HCl, have dipole moments.
Electric field lines of a dipole
Electric field lines of a dipole
Electric field lines always begin on a positive charge and end on a
negative charge. The number of lines leaving a positive charge or
entering a negative charge is proportional to the magnitude of the
charge.
Electric field of two like
point charges
18.8. The Electric Field
Inside a Conductor:
Shielding
18.8. The Electric Field
Inside a Conductor:
Shielding
At electrostatic equilibrium:
1. Any excess charge resides on the
surface.
2. The electric field is zero inside the
conductor.
Conductor in Electric
Field
Conductor in Electric
Field
Under electrostatic equilibrium:
1. The conductor shields the electric field.
2. The electric field just outside the surface a conductor is
perpendicular to the surface.
Conductor in Electric
Field
“Stray” electric fields are produced by various electrical appliances
(e.g., hair driers, blenders, and vacuum cleaners), and these fields
can interfere with the operation of sensitive electronic circuits,
such as those in stereo amplifiers, televisions, and computers. To
eliminate such interference, circuits are often enclosed within
metal boxes that provide shielding from external fields.
Conceptual Example 13
A charge +q is suspended at the center of a hollow,
electrically neutral, spherical conductor, as Figure 18.31
illustrates. Show that this charge induces (a) a charge of –q
on the interior surface and (b) a charge of +q on the
exterior surface of the conductor.
Conceptual Example 13
A charge +q is suspended at the center of a hollow,
electrically neutral, spherical conductor, as Figure 18.31
illustrates. Show that this charge induces (a) a charge of –q
on the interior surface and (b) a charge of +q on the
exterior surface of the conductor.
Copying Machine
Laser Printer
Inkjet Printer