Download Electric Fields 21.1

Electric Fields
Chapter 21
21.1 Creating & Measuring Electric
Fields
The electric force varies inversely as the
square of the distance between two point
objects.
 How can a force be exerted through empty
space?
 Michael Faraday suggested because of an
electrically charged object changing the
properties of space

Electric Field
The changed property of space is the electric
field
 The electric field means that the interaction is
not between two objects, but between an
object and the field at the location of the
object.

Electric Field
How is the electric field measured?
 Place a small positively charged object in the
space, if there is a force on the object, there
is an electric field.
 According to Coulomb’s law the force and the
charge are directly proportional.
 So divide F by q (test charge) and get a
vector quantity representing the electric field
at a certain point.

Electric Field Strength
The direction of an
electric field is the
direction of the force
on a positive test
charge.
 The magnitude of
the electric field is
measured in N/C.

E
Fonq'
q'
Picturing the Electric Field
Electric field is a vector quantity so use an
arrow to represent the direction of a positive
test charge and the number of arrows and
spacing between lines represent the strength
 These are electric field lines
