Download Electric Potential

Physics Lesson Plan
Teacher
Howard
Unit Title
Length
Goal(s)/PLO(s):
Course
Grade Level
Block/Period
J3 calculate electric potential energy and
change in electric potential energy
 define electric potential energy and change in
electric potential energy
 solve problems that deal with two point
charges at rest and that involve
– electric potential energy
– charge
– distance of separation
Phys 12
12
Date
Class Size
Lesson #, of
17-01
 solve problems that deal with two point
charges where one is moved and that involve
– change in electric potential energy
– distance of separation (initial and final)
– charge
Materials:
Timeline
Class Activities
Introduction
Body
Notes 17-01…17-04
Closure
Questions 1-10, 12-13, Problems1-13 odd
17-01 Electric Potential Energy and Potential Difference
Electric potential energy is a conservative force
• The work done by the electrostatic force depends on position
of particles, not the paths taken
The change in potential energy between
two points (a and b) is equal to the
negative work done to move the object
from a to b.
∆PE = -W
If we move a positive point charge
within a uniform electric field (like
between two charged plates) then
W = Fd =qEd
The change in electric potential energy is the negative of the work
done by the electric force
PE b -PE a =-qEd
Electric potential energy decreases. Energy is conserved and the
kinetic energy increases.
Electric Potential
The electric potential energy per unit charge
Only differences in potential energy have any physical meaning
Potential Difference
• The difference in electric potential from point a to b
• The negative of the work done by the electric field to move a
charge from a to b
or
from your data book
The unit of electric potential is the joules/coulomb or the Volt (V)
Remember that we must define a zero point for potential energy,
and it is the changes that matter.
• The ground (earth) is usually defined as zero
Example 17-1
You can use gravity analogies to understand how different
positions result in different potentials
• Keep in mind that there are two types of charge so moving a
positive charge from a to b will give the opposite ∆V as
moving a negative charge
Batteries and generators are designed to maintain a constant
potential difference and different devices draw different amounts
of charge.
Example 17-2
17-02 Relation between Electric Potential and Electric Field
For a uniform electric field (between 2 charged plates) the work
done to move a positive charge is equal to the negative change in
potential energy.
W=-PE=-q∆V
and
W=Fd=qEd
-q∆V = qEd
∆V = -Ed
• your sheet omits the negative sign
Example 17-3
17-3 Equipotential Lines
Equipotential lines can be drawn to represent the electric potential.
charges-and-fields_en.jar
• Equipotential lines and electric field lines are perpendicular
• E points to lower values of V
• Equipotential lines are continuous (no start or end)
17-04 Electric potential Due to Point Charges
When dealing with small numbers of electrons, protons or
molecules, joules are too big a unit.
Electron volt (eV)
The energy acquired by a particle carrying a charge whose
magnitude equals that on the electron (q=e) as a result of moving
through a potential difference of 1V
∆PE=qV
1eV=(1.6E-19C)(1.0V)=1.6E-19 J
• The eV is not a proper SI unit and should not be used in your
calculations
o Convert to Joules first
Questions 1-10, 12-13
Problems1-13 odd