Electric Field
• magnitude of the electric force on a
small, positive test charge divided by the
magnitude of that test charge
• direction of the electric force on a small,
positive test charge
•E=F
e
/ qo
Electric and
Gravitational Fields
• magnitude of the electric force on a small, positive test
charge divided by the magnitude of that test charge
• direction of the electric force on a small, positive test
charge
• E=F /q
• magnitude of the gravitational force on an object divided
electric
0
by the mass of that object
• direction of the gravitational force on the object
• g=F /m
g
0
Electrical Potential
Energy
• potential energy associated with a
charge due to its position in an electric
field
• PE
electric
= Felectric d = q E d (for uniform
field)
• PE
electric:
electrical potential energy (J); q:
charge (C); E: electric field (N/C); d:
displacement in direction of field (m)
Electrical and
Gravitational Potential
Energy
• potential energy associated with a charge due to its
position in an electric field
• PE
e
= Fe d = q E d
• potential energy associated with an object due to its
position in a gravitational field
• PE
g
= Fg h = m g h
•
•
•
•
Electrical and
Gravitational Potential
Energy
as positive charge moves towards the positive end of the field,
work is done on the field and the charge gains potential energy
as positive charge moves away from the positive end of the field,
work is done by the field and the charge loses potential energy
as object moves up, work is done on the field and the object gains
potential energy
as object falls, work is done by the field and the object loses
potential energy
Electric Potential
• the work that must be performed against
electric forces to move a charge from a
reference point to the point in question,
divided by the charge
• V = PE / q = E d (for uniform field)
• V: potential difference (V); PE : electrical
electric
electric
potential energy (J); q: charge (C)
• volt (V) = 1 J/C
Electric and Gravitational
Potential
• the work that must be performed against electric
forces to move a charge from a reference point to the
point in question, divided by the charge
• V = PE
electric
/q=Ed
• the work that must be performed against gravitational
forces to move an object from a reference point to the
point in question, divided by the mass of the object
• gravitational potential = PE
g
/m=gh
Potential Difference
(Voltage)
• the work that must be performed against
electric forces to move a charge between the
two points in question, divided by the charge
• ΔV = ΔPE
electric
/ q = E d (for uniform field)
Electric and Gravitational
Potential Difference
• the work that must be performed against electric forces to
move a charge between the two points in question,
divided by the charge
• ΔV = ΔPE
electric
/q = E d
• the work that must be performed against gravitational
forces to move an object between the two points in
question, divided by the mass of the object
• gravitational potential difference =
ΔPEg / m = g Δh
Equipotential Plots
Electron Volt
• energy acquired by a particle carrying a
charge equal to that on the electron as a
result of moving through a potential
difference of 1 Volt
• ΔPE = q V = (1.6 x 10 C) (1 V)
• 1.6 x 10 J = 1 eV
• not a proper SI unit; still use Joules in
-19
-19
equations
Electric Potential of a
Point Charge
•E=kQ/r
•V=ΣEd
• (integral calculus magic)
• V = k Q / r (where potential is 0 at ∞)
2
Electric Potential
• is a scalar
• much easier to determine electric
potential due to multiple charges
• need to keep track of sign