Download - Physics Day 15
Physics Day 15LO: Discover how work is done and potential
energy is stored in an electric field.
LO: Define electric potential and potential difference.
AGENDA
Do Now
Notes
Worksheet
HW05 Thursday
Do Now: 1.Pick up Electric Circuits Lab Sheet2.Do “PHET” Lab
Electric Potential Energy
A Kiwi Question
• Kiwi (mass 9 kg) illegally climbs onto Mrs. B’s dining room table 1.3 meters high.
• How much work did Kiwi do?• What is his PE on the table?
The Kiwi Answer
• Work = Force x Distance
• Work = mg x h
• PE = mgh
Now with Electricity
• How much work is done moving particle “q” from A to B?
• What is the change in Potential energy?
Now with Electricity
• Work = F. d• F = E.q• Work = E.q.d
Work and Potential Energy
• There is a uniform field between the two plates
• As the positive charge moves from A to B, work is done
• WAB=F d=q E d
• ΔPE =-W AB=-q E d– only for a uniform field
Electric Potential Difference
•But what is the work per unit charge?
WAB=F d=q E d
WAB/q = E d
We call this Electric Potential and it is measured in Volts
Electric Potential Difference
Volts = Work/q = PE/q
Problem
• When a charge of -4e-3C is moved between two points in an electric field, 0.8 joules of work is done on the charge.
• Calculate the potential difference between those two points.
Electron Volts.q V
The “electron volt”, eV is a common unit for energy in particle physics. It is the amount of kinetic energy that an electron obtains when it is accelerated by a potential difference of one volt:
Note that the product:
19 19J1 eV= 1V 1.60 10 C 1 1.60 10 JCe
has units of energy
Multiple of eV Abbreviation
106 MeV
109 GeV
1012 TeV
Problem 2
• Calculate the work done on an elementary charge that is moved between two points in an electric field with a potential difference of 2 Volts?
Unit Pit Stop
Potential
Energy
Electric Field
CJV
mNJ
mVmN
J
J
CV
C
NCN
.
.
JCJCVeeV 1919 106.11106.111 Electron-Volt
Problem 3
• A charge, equal to 2e7 elementary charges, is moved through a potential difference of 300 volts.
• What is the change in potential energy?