Concept Summary
Batesville High School Physics
Electric Fields
 An
electric charge creates a disturbance
in the space around it - an electric
field.
 The electric field extends infinitely far
but weakens with distance.
 This electric field exerts a force on
other charges within the field.
Electric Fields
 Electric
fields are vector fields.
 Direction
at any point is the direction that
a positive charge would move if placed
there.
 Magnitude at any point, E = F/q

Units of E are Newtons/Coulomb
 Force
a charge feels, F = qE
Electric Field Lines
 Point
in the direction a positive
charge would move
 Field is stronger where field lines are
closer together.
 Also called “lines of force”
Charged Conductors
 If
a conductor has a static charge:
 All
of the charge resides on the surface
of the conductor
 The electric field everywhere inside the
conductor is zero.
 If the conductor is not spherical, the charge
distribution will not be uniform.
Electric Potential Energy
 You
have to do work to move a charge
in an electric field.
 The electric potential energy of a charge
at a point in an electric field = -(work
done by the electric field when the
charge is moved there).
Electric Potential
 Electric
potential = electric potential
energy per unit charge
 Electric
potential, V = EPE/q
 Units: Joule/Coulomb

1 Volt = 1 Joule/Coulomb
 Electric
potential is commonly called
voltage .
Voltage
 A location
can have a voltage whether
or not a charge is located there.
 The voltage difference (potential
difference) between two points tells
you:
 The
energy available when a unit charge
is moved between the points, or
 The work that needs to be done to move
a unit charge between the two points.
Voltage
 The
voltage between two points
(potential difference) tells you the
amount of energy 1 Coulomb of charge
will lose when it moves between the two
points.
Storing Electrical Energy
 Since
unlike charges attract, it takes
work to separate unlike charges.
 This work is stored as electrical
potential energy
Capacitors

A capacitor is a device that contains 2 parallel
conducting “plates” insulated from each
other.
 It is used to store electrical energy, by
holding positive charges on one plate and
negative charges on the other.
 Capacitors can be charged to high voltages
and store large amounts of energy.
Van de Graaff Generator
 The
Van de Graaff Generator is a
device for creating large voltages.
 Voltages of 150,000 V + are common
Voltage and Danger
 ENERGY
DOES WORK!
 The Van de Graaff gives each charge a
large amount of energy (high voltage),
but there aren’t many charges therefore the Van de Graaff delivers
very little total energy.
Voltage and Danger
 An
electrical outlet (120 Volts) gives
comparatively little energy to a charge,
but it can deliver LOTS of charge - at
least 15 Coulombs of charge per
second.
 Therefore, the electrical outlet can
deliver LOTS of energy - enough to kill
you!
The End