Download Unit 1 Day 5 – Electric Field Lines

Day 5: Objectives
• Electric Field Lines
– Point Charges
– Electric Diploes
– Parallel Plates
•
Electrostatic Fields and Conductors
Electric Field Lines
• An electric field is a vector quantity
• An electric field of a (+) point charge
points radially outward as lines of force
• An electric field of a (-) point charge points
radially inward
Electric Field Lines
•The distribution of the electric field is called
a vector field
•The number of field lines plotted is
proportional to the magnitude of the charge.
•The nearer the charge, the stronger the
electric field ( F α 1/r2 )
The Electric Dipole
•The electric field produced by 2 point charges
of equal magnitude but opposite sign is called
an electric dipole.
• Electric field lines are directed from (+) to (-) and
start out perpendicular to the surface of the
charge
Parallel Plates
• In the central region of the
electric field between two
closely spaced, oppositely
charged parallel plates, the
magnitude is the same at all
points and is:

E
0
Electrostatic Fields & Conductors
• The static electric field inside a conductor
is zero – if it were not, the charges would
move.
• The net charge on a conductor resides on
its outer surface.
Electric Fields & Conductors
•
•
Free electric charges (electrons) move
until they reach positions where the
electric field, & therefore, the electric
force on them becomes zero.
(They raise to the surface to repel each
other)
Electric fields are always perpendicular to
the outside surface of the conductor
Electrostatic Fields & Conductors
•A metal box or cage can be used as an
effective device against external fields. This is
called a Faraday Cage