Download Section 3: Electrical Potential Energy and Capacitance

Section 3: Electrical Potential
Energy and Capacitance
Gravitational vs. Electrical Potential Energy
Voltage or Electrical Potential
Sample Problem: Find the electric
potential energy and electric potential
Voltage may also be thought of as
“electrical pressure”
Voltage always runs for high concentration of electrons to low
concentration of electrons
Read more on voltage:
http://amasci.com/miscon/voltage.html
Capacitors: Device that stores charge
Activity: Dissecting a capacitor and find
out how it stores charge.
1) Draw a picture of the internal parts of
a capacitor.
2) Use you picture to describe how it
works.
3) One sheet per group.
Parts of a Parallel Plate Capacitor
1) Plates – location where
opposite charges are
stored
2) Dielectic – Separates the
charge and increase the
ability to store charge
“capacitance”
Design your own capacitor
Materials: Aluminum foil and 4 cups
Requirements:
1) Must have electrodes to hook up to.
2) Must work for full credit otherwise try again
Grading: 15 pts
1) Works and does not arc to itself (15pts)
2) Works and arcs to self (12 pts)
3) Does not work (0 pts) keep trying
Capacitor Reflection
1) Describe how a capacitor works.
2) Describe how you assembled your
capacitor.
3) What flaws did you find in your
capacitor?
4) List three things you could have done
to make your capacitor stronger?
Capacitors and Potential Energy:
Capacitance (C): Ability to
store charge
C = εo A/d
εo – permittivity
(8.85 x 10-12 C2/N•m2)
Charge on Capacitor (Q):
Q = CV
Potential Energy PEe:
PEe = ½(Q)V
Sample Problems
1) Find the charge on a capacitor that has
a capacitance of 2μf ( 2 micro farads)
at 30 volts:
2) If the distance between the plates of a
capacitor is .0005m, find its surface
area to have one farad of capacitance.
3) Find the potential energy stored in a
5μf capacitor that is charged with 10
volts.
4) Find the surface area charge on the
capacitor above.
Activity: Finding the capacitance of a
capacitor
Procedure:
1) Charge a capacitor and then discharge it
through a resistor (yellow).
2) Graph current (Coulombs/second) to find the
total charge.
3) Use C = Q/V and compare the value on the
capacitor.
4) Calculate the percent error.