3. Unlike charges ATTRACT

4. Like charges REPEL

6. + FORCE We define the direction of the electric field at a particular place as being the direction of the force it produces on A POSITIVELY CHARGED OBJECT Example:Charge and Field Electric Force

8. Electric field of two charges system

12. Drawing/mapping electric field lines

15. Rules for Drawing Electric Field Patterns There are a variety of conventions and rules to drawing such patterns of electric field lines. The conventions are simply established in order that electric field line patterns communicate the greatest amount of information about the nature of the electric field surrounding a charged object. One common convention is to surround more charged objects by more lines. Objects with greater charge create stronger electric fields. By surrounding a highly charged object with more lines, one can communicate the strength of an electric field in the space surrounding a charged object by the line density. This convention is depicted in the diagram below.

16. ++++++++++ ---------- The lines are equally spaced Showing the electric force between The plates are constant

18. mg h

19. ++++ ---- ++

28. EXAMPLE

30. v p = 9.3 x 10 4 m/s

31. Example

35. A tiny ball of mass 0.60 g carries charge of magnitude 8  C. It is suspended by a thread in a downward electric field of intensity 300 N/C. What is the tension in the thread if the charge on the ball is (a) POSITIVE (b) NEGATIVE? Tension, T E Field Example

36. T E Field qE weight T E Field qE weight + -

37. Definition of Electric Field An electric field is a region of space where an electric charge experiences an electrostatic force. The strength of the field is the ratio of the force experienced by the charge to the magnitude of the charge. The direction of the electric field is the direction of the force that would be experienced by a small postitive charge placed at that point. Electric field intensity (sometimes just called electric field) is the force per unit charge experienced by a point charge somewhere in space. E = F/q Therefore, F = Eq Concept of Field Region throughout which a force may be exerted; examples are the gravitational, electric, and magnetic fields that surround, respectively, masses, electric charges, and magnets. Fields are used to describe all cases where two bodies separated in space exert a force on each other.

38. Electric Potential Energy The amount of energy required to move a charge from point to another within a region of electric field. EPE = Work done in moving the charge = (force)(displacement) = (qE)d Electric Potential and Potential Difference (Voltage) The amount of EPE per charge is the definition of electric potential. The difference in electric potential between any two point defines the Voltage. Conservation of Energy In a closed system, the amount of EPE possessed by the charge in moving between any two points will be converted into other forms of energy, i.e. Kinetic energy. qEd = qV = ½ m v 2

39. UNIFORM ELECTRIC FIELDS The field is uniform and constant except near the edge of the plates Since Electric Field Strength (E) is constant F = qE, the force on any charge q between the plates is also constant.  If the force acting is constant, any free charge of mass m, between the parallel plates would experience a constant acceleration, a (Newton’s Law) a = F/m We could use the equations of constant accelerated motion to solve problems

42. Deflection of Charge

47. SOLUTION: Example

48. An electron (q = 1.6 x 10 -19 C, m = 9.1 x 10 -31 kg) is projected out along the +x axis with an initial speed of 3 x 10 6 m/s. It goes 45 cm and stops due to uniform electric field in the region. Find the magnitude and direction of the field.

49. An electron is shot at 10 6 m/s between two parallel charged plates. If Electric field strength between the plates is 1 kN/C, where will the electron strike the upper plate? Assume vacuum conditions.