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?