2. V (in Volts) = Potential EPE (in Joules) = Electric Potential Energy
Make sure that we understand the difference between Potential and Electric Potential Energy:
V (in Volts) = Potential
a property of a certain position in an Electric Field with or without charges placed there E -
EPE (in Joules) = Electric Potential Energy
a property of charges placed at a certain position in an external Electric Field + E

3. Conservation of Energy
in an Electric Field
If a charged particle gains kinetic energy in an electric field, it loses an equivalent amount of potential energy.
Point B is at a lower electric potential than is point A.
Points B and C are at the same electric potential.
The gain in kinetic energy depends only on the potential difference and not the path taken.

5. An electron acquires x J of kinetic energy when it is accelerated by an electric field from plate A to plate B.
What is the potential difference and which plate is at the higher potential? A B E
Plate B has a positive charge
and is at a higher potential.

6. x =1.00 cm q = 1.60 x C
E = 2000 N/C m = 9.1 x kg q m x E
[2] a) Find the speed of the
charge at the lower plate.
b) Find the potential through
which the charge moves.

7. E q x m
x =1.00 cm q = 1.60 x C
E = 2000 N/C m = 9.1 x kg
d) Find the acceleration of the charge.
c) Find the force on the charge
as it moves. or

8. Electric Potential Due to Point Charges
What is the Potential at this point? q
Notes:
1) Include the sign of q in your calculation! (+ or -)
2) Potential Difference can also be calculated:
V = V2 – V1
3) The equation can also be used for a charged sphere: + r
Total charge
Distance from center
4) Electric Potential is a scalar not a vector
V = V1 + V2 + V3 + … (an algebraic sum, not a vector sum)

9. Electric Potential due to a System of Point Charges
For a system of point charges Qi at distances ri from a point P: Q1 Q4 Q3 Q2 P r1 r2 r3 r4
… an algebraic sum of scalars!

10. Electric Potential Due to Point Charges
Electric potential at a
distance r from a positive charge Q
Electric potential at a
distance r from a negative charge Q

14. [4]What is the electric potential at a distance of 2
[4]What is the electric potential at a distance of x m away from a proton? +q -q P d
[5] Find the potential V at point P due to the four charges.

15. [6] The +4 μC charge is located at 4 m on the x-axis and the -6 μC is located at +2 m on the y-axis as shown below.
Calculate the magnitude and determine the direction of the electric fields at the origin due to the +4 μC charge and due to the -6 μC charge.
b) Calculate the electric potential at the origin.
c) Calculate the work done to bring a +4 μC from infinity to the origin.
Ans: N/C, 100o from +ve x axis; -18,000 V; J