Electric Potential and Electric Potential EnergyA.S. 5.1.1 – 5.1.4 due MondayReading reference: chapter 16

Question 16.1a Electric Potential Energy I

a) protonb) electronc) both feel the same forced) neither – there is no forcee) they feel the same magnitude

force but opposite direction

E

electron

proton

E

Electron

Proton+

-

A proton and an electron are in a constant electric field created by oppositely charged plates. You release the proton from the positive side and the electron from the negative side. Which feels the larger electric force?

Question 16.1a Electric Potential Energy I

a) protonb) electronc) both feel the same forced) neither – there is no forcee) they feel the same magnitude

force but opposite direction

E

electron

proton

E

Electron

Proton+

-

Since F = qE and the proton and electron have the same charge in magnitude, they both experience the same force. However, the forces point in opposite directions because the proton and electron are oppositely charged.

A proton and an electron are in a constant electric field created by oppositely charged plates. You release the proton from the positive side and the electron from the negative side. Which feels the larger electric force?

E

electron

proton

E

Electron

Proton +

-

a) protonb) electronc) both feel the same accelerationd) neither – there is no acceleratione) they feel the same magnitude

acceleration but opposite direction

A proton and an electron are in a constant electric field created by oppositely charged plates. You release the proton from the positive side and the electron from the negative side. Which has the larger acceleration?

Question 16.1b Electric Potential Energy II

E

electron

proton

E

Electron

Proton+

-

a) protonb) electronc) both feel the same accelerationd) neither – there is no acceleratione) they feel the same magnitude

acceleration but opposite direction

Since F = ma and the electron is much less massive than the proton, the electron experiences the larger acceleration.

A proton and an electron are in a constant electric field created by oppositely charged plates. You release the proton from the positive side and the electron from the negative side. Which has the larger acceleration?

Question 16.1b Electric Potential Energy II

E

electron

proton

E

Electron

Proton+

-

a) protonb) electronc) both acquire the same KEd) neither – there is no change of

KEe) they both acquire the same KE

but with opposite signs

Question 16.1c Electric Potential Energy III

A proton and an electron are in a constant electric field created by oppositely charged plates. You release the proton from the positive side and the electron from the negative side. When it strikes the opposite plate, which one has more KE?

E

electron

proton

E

Electron

Proton+

-

a) protonb) electronc) both acquire the same KEd) neither – there is no change of

KEe) they both acquire the same KE

but with opposite signs

Since PE = qV and the proton and electron have the same charge in magnitude, they both have the same electric potential energy initially. Because energy is conserved, they both must have the same kinetic energy after they reach the opposite plate.

Question 16.1c Electric Potential Energy III

A proton and an electron are in a constant electric field created by oppositely charged plates. You release the proton from the positive side and the electron from the negative side. When it strikes the opposite plate, which one has more KE?

Electric Potential Energy• Small group whiteboard task:• On 1 half of the whiteboard:• Draw a diagram of a spherical mass and its gravitational

field lines• Write the equations for gravitational field strength,

gravitational potential energy, and gravitational potential• Discuss the definitions of each of these concepts

• On the other half of the whiteboard:• Draw a diagram of a positive point charge and its electric

field lines• Write the equation for electric field strength• Predict the equations for electric potential energy and

electric potential• Determine a definition for electric potential energy and for

electric potential

Electric Potential Energy• The energy stored in an electric field in the

space between two charged objects.

• Units: Joules / J

𝑈=𝑘𝑞𝑄𝑟

Electric Potential• The work done, per unit positive charge, to move

a positive test charge, q, from infinity to some position, P, away from an object with charge Q.

• Also related to electric field strength:

• And:

• Which also means that:

• Units = Volts / V

𝐸=− ∆𝑉∆ 𝑥

Where is high potential?• If a positive test charge is used as the reference

charge, where would it have the highest potential?•Near a positive chargeor• Near a negative charge

• Why?