Electric Fields and Potential

PhysicsChapter 33

Engagement

• Why is wiring covered with rubber? Use the terms conductor and insulator in your explanation.

Agenda

• Review HW • Note taking• Class work• Q and A• Closing

Electric Field

• Space around every charge• Has magnitude and direction*• Magnitude – how strong• Direction- its response to a (+) charge

Electric Field Lines

• Express electric field with vectors• Length of line = strength• Direction of arrow = response to (+) charge

Check for Understanding

• Why are the field lines drawn away from the (+) charge and toward the ( - ) charge?

Electric Potential Energy

• Energy of a charged based on location• Exertion of work by an external force adds

potential energy to object

Electric Potential Energy

Moving from A to B

Moving the (+) test charge from location A to B requires work b/c goes against E therefore increases in PE of charge

Moving the (+) test charge from location B to A is in the direction of the electric field so PE decreases since no work needed

Moving from B to A

Electric Potential Energy

Moving from A to B

Moving the (+) test charge from location B to A requires work b/c goes against E therefore increases in PE of charge

Moving the (+) test charge from location A to B is in the direction of the electric field so PE decreases since no work needed

Moving from B to A

Electric Potential

• Different from electric potential energy• The electric potential energy per charge• Units are volts (V)• Often called voltage

Electric Potential =

V =

Check for Understanding

• What is the difference between voltage and electric potential?

Nothing, they are the same thing.

Reach for the StarsIf V = and V is the electric potential measured in volts, then how can 1 volt be expressed in alternate units?

Measurement Symbol Units

Electric potential

V V (volts)

Electric potential energy

PE J (Joules)

Charge q C (Coulombs)

1 volt = 1 joule coulomb

Understanding Electric Potential or Voltage

• 1 volt = 1 J of energy per coulomb charge• 1000 volts = 1000 J of energy per coulomb charge

High voltage DOES NOT mean danger

*high voltage requires high energy and a lot of charge.*Often very little charge is involved; therefore, little energy is required and the electric potential/voltage is small

Class work / Homework• Make sense of all these terms. Consider rubbing the

balloon on your hair and it sticking to the wall. Explain how this works, using the following terms/ideas

1. Charge by friction2. Charge by polarization3. Electric potential energy4. Electric potential5. There is voltage but very little

Use the notes and chapter 32 and 33 in the book to help.

Closing

• In order for a particle to have voltage, what must the particle have?

• Draw the electric field around the charges

+ _