1. Electric Fields

2. What You Will Learn An electric field is like a.An electric field is like a. An electric field is a.An electric field is a. An electric field provides the that a will move if placed in the field.An electric field provides the that a will move if placed in the field. An electric field is composed of a series of imaginary.An electric field is composed of a series of imaginary.

3. What you already know Coulomb’s Law:Coulomb’s Law: Note: is much smaller than ! F +

4. Electric Field The electric field is the that a experiences divided by itself. Note: The electric field is a and therefore has magnitude and direction. F +

5. What is the It is enough that it does not affect the field due to other charged objects. It will move towards or away from other charged objects depending on whether it is charged similarly or dissimilarly from other objects.

6. The Test Charge (Cont.) + + + + + + + + + + + + + + + + + + __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Positively Charged Object Negatively Charged Object Test Charge moves from a positively charged object Test Charge moves a negatively charged object

7. Example A positive charge of 4.0 x 10 -5 C experiences a force of 0.36 N when located at a certain point. What is the electric field intensity at that point? Note: The says nothing about the magnitude of charge, which is the of the that produces the that charge experiences.

8. Electric Field Lines Electric field lines, or of, provide a of the at any point in space from a charge.Electric field lines, or of, provide a of the at any point in space from a charge. Electric field lines show the that a would take if placed in the field.Electric field lines show the that a would take if placed in the field. + + + + + + + + + + + + + + + + + + __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

9. Electric Field Lines Electric field lines at and are always directed away from them towards.Electric field lines at and are always directed away from them towards. Electric field lines do or except at the of or charges.Electric field lines do or except at the of or charges. Electric field lines are ( ) to the where they or.Electric field lines are ( ) to the where they or. Electric field lines.Electric field lines. The strength of the field is proportional to the magnitude of the charge and is directly related to the of field linesThe strength of the field is proportional to the magnitude of the charge and is directly related to the of field lines the there are and the together they are, the the field.the there are and the together they are, the the field.

10. Electric Field Lines Due to a Point Charge + + + + + + + + + + + + + + + + + + Direction of field is. Lines intersect. Density of lines is.

11. Electric Dipole + + + + + + + + + + + + + + + + + + __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Note: Force on a ( ) is the field lines, and is the of the forces due to of the dipole acting on it. Note: An electric dipole consists of in and in.

12. Examples from the Web http://www.cco.caltech.edu/~phys1/java/phys1/EField/EField.html http://phet.colorado.edu/sims/charges-and-fields/charges-and-fields_en.html

13. Electric Fields and Conductors At equilibrium, excess charges will reside on the of a conductor.At equilibrium, excess charges will reside on the of a conductor. The electric field is at any point within a conducting material at.The electric field is at any point within a conducting material at. Charge within a conductor is from external electric fields because they or on the where excess charges reside.Charge within a conductor is from external electric fields because they or on the where excess charges reside. E E-Field inside conductor + + + + + + + + + + + + + + + + + +

14. Parallel Plate Capacitor The parallel plate capacitor is an device used in all kinds of electronics.The parallel plate capacitor is an device used in all kinds of electronics. Field lines in a parallel plate capacitor are and to one another, indicating a electric field.Field lines in a parallel plate capacitor are and to one another, indicating a electric field. ++++++++ --------

15. Electrostatic Force and Distance For point charges:For point charges: The strength of the field as the distance.The strength of the field as the distance. + + + + + + + + + + + + + + + + + +

16. Electrostatic Force and Distance For parallel plates:For parallel plates: The strength of the field is from one plate to the other.The strength of the field is from one plate to the other. Since, the will be.Since, the will be.

17. Force and Electric Field Strength vs. Distance Point ChargeParallel Plate Distance

18. Example (Millikan Oil Drop Exp.) An oil drop is negatively charged and weighs 8.5 x 10 -14 N. The drop is suspended in an electric field intensity of 5.3 x 10 1 N/C. What is the charge on the drop? How many electrons is that?

19. Key Ideas Electric fields exists around any conductor or insulator that contains a charge.Electric fields exists around any conductor or insulator that contains a charge. The electric field intensity is a measure of the force on a test charge placed in the field.The electric field intensity is a measure of the force on a test charge placed in the field. The strength of the field is proportional to the density of field lines.The strength of the field is proportional to the density of field lines. Field lines are perpendicular to all charged surfaces.Field lines are perpendicular to all charged surfaces. The electric field is always directed away from positive charges and towards negative charges.The electric field is always directed away from positive charges and towards negative charges.