I.)
Electric Potential -
work needed
or energy acquired
when a positive charge is moved from infinity to a certain point in an
electric field.

II) Potential Difference
(Voltage)
potential energy difference between 2 points in an electric field per
unit of charge

A) Potential
Difference, Energy & Work

As a charge moves through an
electric field it gains PE or KE

If "Opposites" move

Closer

Gain KE or PE?

They Gain KE

If 'Opposites' Separate

Gain KE or PE?

They Gain PE

If "Likes" Separate

Gain KE or PE?

They Gain KE

If 'Likes' move closer

Gain KE or PE?

They Gain PE

1) Equation #1

Charge q moving between 2 points in a field

V =

W

(Joules)

q

(Coulombs)

W
= work done
against field orenergy acquired
working with field (Joules or eV)

eV = electronVolts

(small energy unit)

q
- amount of charge moving through field (Coulombs)

V
- Potential Difference (volts)

AP Physics

Charge q moving between 2 points in a field

U_{E} = PE (W)

V =

U_{E}

(Joules)

q

(Coulombs)

U_{E} = qV = PE between between 2 charges

U_{E} =

kq_{1}q_{2}

r

V =

Kq

r

V - electric potential
(Scalar)

Ex)
It takes 6 J of work to move 2 C of charge between 2 points in an
electric field.

What is the potential energy difference (V)
between these points?

Ex) It takes
6 Joules of work
to move 2 coulombs
of charge
between 2 points in an electric field. What is the potential energy difference
(voltage) between these 2 points?

V =

W

(Joules)

q

(Coulombs)

V
=

6
Joules

2 Coulombs

V
= 3 Volts or J/C

2)
Potential difference Eq. #2

V =

W

(eV)

q

(elementary
charges)

W = work done against field
or energy acquired working with field

(Electronvolts = Ev)

Electronvolt – small energy unit
= 1.6 x 10^{-19} J

q - amount of
charge moving through field (# elementary charges)

V - Potential Difference
(volts)

Ex) It takes 10
eV to move 2 elementary charges from
one point to another in an electric
field.
Find the potential difference between these points.

Ex) It takes
10 eV to move
2 elementary charges
from one point to another in an electric field. Find the potential difference
between these points.

V =

W

(eV)

q

(elementary
charges)

V

=

10
eV

2
elementary
charges

V = 5 Volts

Ex) +2
elementary charges acquire
16 joules of energy when they move between 2
points in an electric field.

What is the
potential difference (voltage)
between these two points in the field?

Ex)+2 elementary charges
acquire 16 joules
of energy when they move between 2 points in an electric field. What is
the potential difference
(voltage) between these two points in the field?

Units don't match!!!

elementary charges, eVJoules/Coulombs

+2 elementary charges =

3.2 x 10^{-19} C

V =

W

(Joules)

q

(Coulombs)

V =

16 J

(3.2 x 10^{-19}
C)

V = 5.0 x 10^{19}
Volts

or J/C

Ex) If 4.8 x 10^{-17}
joules of work is required to move an electron between 2 points
in an electric field, what is the electric potential difference
between these points?

a) 3.0 x 10^{2} V

b) 4.8 x 10^{-17} V

c) 1.6 x 10^{-19} V

d) 4.8 x 10^{2} V

Ex) If
4.8 x 10^{-17}
joule of work
is required to move an
electron between 2 points in an
electric field, what is the electric
potential difference between these points?

a) 3.0 x 10^{2} V

b) 4.8 x 10^{-17} V

c) 1.6 x 10^{-19} V

d) 4.8 x 10^{2} V

W = 4.8 x 10^{-17}
Joule

V = ?

q = ?

Hint: The charge in this
problem is an electron

q = 1.6 x 10^{-19}
C

V =

W

(Joules)

q

(Coulombs)

V = 4.8 x 10^{-17} J / (1.6 x 10^{-19}C)

a) 3.0 x 10^{2} V

AP Physics

Electric Field - Parallel Plates

E = V/d = F/q

Conducting plates are 0.04 m apart, as shown
above. Point P is located 0.01 m above the lower plate.

a. The electric potential at point P is

(A) 10 V (B) 8 V
(C) 6 V (D) 4 V (E) 2 V

E = V/d = 8 V/.04m

= 200 V/m

200 V/m = V/.01m

V = 2 V

(A) 10 V (B) 8 V
(C) 6 V (D) 4 V(E) 2 V

b. The magnitude of the electric field at point P
is