Transcript Electric Field

Electric Field Concept
By:
Engr. Hinesh Kumar
Lecturer
I.B.T, LUMHS
Electric Charge
The effects of electric charge were first observed as static
electricity:
After being rubbed on a piece
of fur, an rod acquires a
charge and can attract small
objects.
Electric Charge
Charging both amber and glass rods shows that there are
two types of electric charge; like charges repel and
opposites attract.
Electric Charge
All electrons have exactly the same charge; the charge
on the proton (in the atomic nucleus) has the same
magnitude but the opposite sign:
Electric Charge
Definition
Electric charge is a physical property of matter that causes it to
experience a force when close to other electrically charged
matter.
There are two kinds of charge.
Properties of Charges
 like charges repel
 unlike charges attract
 charges can move
+
-
The Concept of a Field
A field is defined as a property of space in which a material
object experiences a force.
P
m
Above earth, we say there is a gravitational field
at P.
.
F
Because a mass m experiences a downward
force at that point.
No force, no field; No field, no force!
The direction of the field is determined by the force.
What is a Field?
 In physics, a field is a
physical phenomena that
has a value everywhere in
space.
 Loudness has a value
everywhere around a
stereo.
 This means you can
describe the loudness with a
field.
 All interactions between
matter and energy occur by
way of fields.
Fields and energy
 Any field is a form of
energy that is
distributed through
space.
 A magnetic field has
energy because it can
exert force over
distance, or do work,
on another magnet.
Adding fields
 Fields of the same kind
can be added or
subtracted.
 The field from an
electromagnet can
either cancel the field
from a permanent
magnet or add to it.
Electric Field
 Electric field is defined as
the electric force per unit
charge.
 The direction of the field is
taken to be the direction of the
force it would exert on a
positive test charge.
 The electric field is radially
outward from a positive
charge and radially in toward
a negative point charge
Electric Field
Here, q0 is a “test charge” – it serves to allow the
electric force to be measured, but is not large
enough to create a significant force on any other
charges.
Electric Field
If we know the electric field, we can calculate the force on any
charge:
The direction of the force
depends on the sign of the
charge – in the direction of the
field for a positive charge,
opposite to it for a negative
one.
Drawing the Electric Field
 Electric field lines follow
the direction of the force on
a positive test charge.
 The strength of the electric
field is shown by the
spacing of the field lines.
 The field is strong where
the field lines are close
together and weak where
the lines are far apart.
Electric Field Lines
The charge on the right is twice the magnitude of the charge on the left (and
opposite in sign), so there are twice as many field lines, and they point towards
the charge rather than away from it.
Electric Field Lines
Combinations of charges. Note that, while the lines are less dense
where the field is weaker, the field is not necessarily zero where
there are no lines.
In fact, there is only one point within the figures below where the
field is zero – can you find it?
Answer
 the field from a collection of charges is simply
the vector sum of the fields from the individual
charges. To find the places where the field is
zero, simply add the field from the first charge
to that of the second charge and see where
they cancel each other out
 According to this explanation:

Field is zero in figure 3.

http://physics.bu.edu/~duffy/py106/Electricfield.
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