Ele

ctric vs. G

ravita

tional

Pote

ntia

l Energ

y

• Work is needed to push an object against gravity and give it Potential Energy (PEg)

Gravitational Potential Energy Increases

g

• Work is needed to push a charge against a field and give it Electric Potential Energy

Electric Potential Energy Increases

E

+-

Un

iform

Ele

ctric Field

s

Allesandro Volta(Italian: 1745 – 1827)Parallel Plates

Point charge

Uniform electric field

Note the field lines

Pote

ntia

l En

erg

y &

Pote

ntia

l Diff

ere

nce

–2–

LowPotential Energy

- - - - - - - - -

+++++++++E

HighPotential Energy

LowPotential Energy

HigherPotential Energy

Why does this one have more potential

energy?

Pote

ntia

l En

erg

y &

Pote

ntia

l Diff

ere

nce

2+

- - - - - - - - -

+++++++++E

High or Low PE?

High or Low PE?

A change in PE means …

Pote

ntia

l En

erg

y &

Pote

ntia

l Diff

ere

nce

PotentialDifference

(V)

=ΔElectric Potential Energy

(J)Charge of particle (C)

Potential Difference Voltage (scalar or vector)

ΔPEelectric= qΔV

=ΔV = kQr

What does voltage actually measure?– Measures how much energy a

charge will gain/lose– Measures how much work that can

be done by a charge

Pote

ntia

l En

erg

y &

Pote

ntia

l Diff

ere

nce

–2–

- - - - - - - - -

+++++++++E

Which of these has greater electrical potential

energy per charge?

more ELECTRIC POTENTIAL ENERGY

Same ELECTRIC POTENTIAL

An

alo

gy

12 V0 V

Battery gives the electron 12 J of Potential energy

e “loses” energy as it travels through the circuit.

Battery “gives” energy back to electron to repeat cycle

Four ways to refer to voltage: 1. Electric Potential; units: V 2. Electric Potential Difference; units: V 3. Potential Difference; units: V 4. Voltage; units: V

If the word energy is included then the term refers to electric potential ENERGY and the units are Joules.

Key Id

eas

Electric Potential Energy

Electric Potential,Potential,Voltage

Electric Potential Difference

Defin- ition

Total Potential Energy

Energy per charge

Change in voltage

Unit Joules Volts (V)(J/C)

Volts (V)(J/C)

Equation

PEe= kQq/r = qEd = qV

V = PE/q ΔV = ΔPE/q

Hid

den

Eq

uatio

ns

W = Fd F = kQq/r2

W = (kQq/r2)rW = kQq/r = PEelectric

if PEelectric = W = qV V = kQ/r

V = Edd and r for distance, V for Voltage, W for Work, Q and q for Charge, PE for Potential Energy, F for Force