Electric Potential and Electric Fields

Sections Covered – Chapter 33 Topics Covered – Electric Fields – Electric Field Lines – Electric Shielding – Electric Potential – Electric Potential Energy

The Big Picture Same world, but different ‘lenses’ Consider different ways you can ‘look’ at something

Gravitational Fields vs. Electric Fields We can discuss mass and gravitational fields…

Gravitational Fields vs. Electric Fields …Or we can discuss electric charges and the electric field

Road Map – Where We’re Going Electrostatics Circuits Non-moving Charges Moving Charges Electric Field Electric Potential Electric Potential Energy

Fields Not that kind… A field (in physics) is a quantity that has a value for each point in space and time. Ex. Temperature Field

Electric Field Fields can show direction…. …and magnitude

Electric Field Generated by electric charges, the electric field is a force field filling space around every electric charge. Electric Field - How do you explain/describe something invisible? Charges generate and react to this field.

Electric Field Question asked by Michael Faraday Illustrated ‘lines of force’ Electric field lines

Electric Field Lines Rules Electric Field Lines… 1) Flow away from positive charges…. 2) ….and towards negative charges 3) They move in ALL directions 4) Density of lines = strength of the field 5) Lines don’t stop, don’t intersect

Electric Field Lines Sketch the electric field lines for the charge below

Electric Field How do you know how strong the field is? How could you figure out how fast and which way the water is flowing? Throw something in, see what happens to it Something small…. Two ways…..

Calculating the Electric Field Method #1 We can measure the strength of the electric field based on its affect on other charges. Using a small test charge ◦ E = Electric Field ◦ F = Force experienced by the test charge ◦ q = test charge ◦ SI Unit for Electric Field Newton Coulomb =

Calculating the Electric Field Positive test charges move...with the field Negative test charges move…against the field WHY??

Example 1 An electric field of 2.0 x 10 4 N/C is directed along the positive x-axis. A.What is the magnitude and direction of the electric force on an electron placed in the field? B.What is the magnitude and direction of the electric force on a proton placed in the field?

Example 2 A negative charge of - 1.5×10 -7 C experiences a force of N to the right in an electric field. What is the magnitude and direction of the electric field?