ELECTRIC POTENTIAL AND ENERGY
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Guidelines and tips
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Understanding Electric Potential Energy, Potential, and Capacitors, Lecture notes of Physics
An in-depth exploration of electric potential energy, electric potential, and capacitors. It covers the relationship between electric fields and work, the concept of electric potential as voltage, and the calculation of electric potential and electric field for point charges. Additionally, it discusses the role of capacitors in storing electric energy and the impact of dielectrics on capacitor strength.
Typology: Lecture notes
2021/2022
1 / 12
This page cannot be seen from the preview
Don't miss anything!
Related documents
Partial preview of the text
Download Understanding Electric Potential Energy, Potential, and Capacitors and more Lecture notes Physics in PDF only on Docsity!
ELECTRIC POTENTIAL AND ENERGY
Electric Potential Energy
●
E fields can do work on charged particles
- (^) So they must contain energy
● PE
electric
similar to PE
gravity
( qEd vs. mgd )
- (^) Except it can be attractive or repulsive
- (^) General rule: forces push toward lowest possible PE F = qE Work = Fd = qEd E field d
High PE
Low PE
Very Low PE
U and V for Point Charges
● U needs reference point → like “floor” in PE
gravity
- (^) Convention for point charges:
- (^) Infinite separation is the “zero” of U and V
- (^) U and V can be + or – , depending on charges ●
For more than 2 charges:
– V
total = sum of V's from each charge
- U total = sum of U's from each pair of charges U = k qq ' r r
q q'
V = k q r
Point Charge Equations
F = k
q
1
q
2
r
2 E = k ∣ q ∣ r 2 U = k qq ' r V = k q r
E =
F
q
V =
U
q '
F = −
U
x E = −
V
s
Capacitors
C = 0 A d Capacitance C = Q V E = V d
V = V
b
− V
a 0 =^ 8.85∗^10
− 12 C
V ⋅ m Units: Farad (F) = 1 C/V
Energy Storage in Capacitors
●
Capacitors store potential energy in the E field
- (^) 3 ways to express energy: ●
If capacitor is connected to a battery:
- (^) V = constant → Q can change if C changes ●
If capacitor is disconnected:
- (^) Q = constant → V can change if C changes
U =
C V
2 U =
Q
2 C
U =
Q V
Dielectrics – Making Capacitors Stronger
● Put an insulator (with “bound electrons”) in an E field
- (^) e– are not “free” → shape of the electron cloud is affected
● Atom is now “polarized” → energy is stored like a spring
- (^) Can make capacitors stronger by inserting these “dielectrics” ● (^) Too much polarization → electron separates from nucleus
- (^) “Dielectric breakdown” – material becomes a conductor
Capacitors with Dielectrics
●
Every material has 2 dielectric properties:
- (^) “Dielectric constant” K
- (^) “Dielectric strength” → E field at which breakdown occurs ●
Capacitance with dielectric
- (^) Is K times bigger ●
Increase in C → change in U
- (^) Depends on whether capacitor is connected to battery
C = KC
0