Electric Field. Electric Field & Potential. Comparing Fields. Find Fe. Electric field due to a single point-like charged object

Transcription

1 10/7/014 Electic Field Electic Field & Potential Physics 115 Eyes Foce pe Unit test chage: A Ratio F E = Fom Coulomb s Law q0byq q0 kqq E = q 0 0 kq E = Electic Fields Compaing Fields Gavitatial Fields Electic field due to a single point-like chaged object kqbyq kqby q Eq Gmbym Gmby m gm 014 Peas Educati, Inc. Using the supepositi pinciple Find Fe Find the Electic Foce q1 caused by the q and q3. q1= q = 4 µc q3 = q4= -3 µc q1 q4 q R1=5 m R13=8m q3 6 m 014 Peas Educati, Inc. 1

2 10/7/014 Finish the poblem Find Ee F 1 degees W of N (4x10 (4x10 C 5 m Negative 5.75x10-3 sin 37º= -3.46x10-3 Positive 5.75x10-3 cos37º= +4.6x10-3 F 1 by degees Zeo Negative -1.69x10-3 (4x10 (3x10 C Resultant -3.46x x10-3 F 1 by and 3 = 4.5x º above x axis Find the Electic Field at locati p caused by the q and q3. q = 4 µc q3 = q4= -3 µc R1=5 m R13=8m p q4 q3 q 6 m Finish the poblem E at 1 degees W of N (4x10 E = C 5 m Eat 1 by -90 degees (3x10 E = C Resultant E at 1 by and 3 = E field lines Field Lines Electic Field Gavitatial Field 014 Peas Educati, Inc. Fig , p.399

3 10/7/014 E field lines Simulatis mulatis/simusoft_efi eld.html u/sims/chages-andfields/chages-andfields_en.html 014 Peas Educati, Inc. Electic potential due to a single chaged object 014 Peas Educati, Inc. Quantitative Execise 15.6 Suppose that the heat's dipole chages Q and +Q ae sepaated by distance d. Wite an expessi fo the Vfield due to both chages at point A, a distance dto the ight of the +Qchage. 1. Simplify and diagam.. Repesent mathematically., =, = + Add: = 014 Peas Educati, Inc. 1 + = Potential diffeence The value of the electic potential depends the choice of zeo level, so we often use the diffeence in electic potential between two points. 014 Peas Educati, Inc. 3

4 10/7/014 Checking Undestanding Change in Electic Potential =! =! = #$ %& - #$ %& ' ( ' ) =!! = = Rank in ode, fom lagest to smallest, the electic potentials at the numbeed points. HINT: = Copyight 007, Peas Educati, Inc., Publishing as Peas Addis-Wesley. A pot has a speed of 3.5 x 10 5 m/s at a point whee the electical potential is 600 V. It moves though a point whee the electic potential is 1000 V. What is its speed at this secd point? Its about Enegy! How do you know? Equipotential sufaces: Repesenting the Vfield The lines epesent sufaces of cstant electic potential V, called equipotential sufaces. The sufaces ae sphees (they look like cicles a twodimensial page). Copyight 007, Peas Educati, Inc., Publishing as Peas Addis-Wesley. 014 Peas Educati, Inc. Ctou maps: An analogy fo equipotential sufaces A Topogaphic Map 014 Peas Educati, Inc. Copyight 007, Peas Educati, Inc., Publishing as Peas Addis-Wesley. 4

5 10/7/014 Gaphical Repesentatis of Electic Potential Cnecting Potential and Field Copyight 007, Peas Educati, Inc., Publishing as Peas Addis-Wesley. Copyight 007, Peas Educati, Inc., Publishing as Peas Addis-Wesley. Potential and Field fo Thee Impotant Cases The Potential Inside a Paallel-Plate Capacito Copyight 007, Peas Educati, Inc., Publishing as Peas Addis-Wesley. +,-./ = Δ Δ0 Slope = E Copyight 007, Peas Educati, Inc., Publishing as Peas Addis-Wesley. A pot is eleased fom est at point a. It then tavels past point b. What is its speed at point b? Its about Enegy! How do you know? (How is this simila to the pevious poblem?) A pot has a speed of 3.5 x 10 5 m/s at a point whee the electical potential is 600 V. It moves though a point whee the electic potential is 1000 V. What is its speed at this secd point? Its about Enegy! How do you know? Copyight 007, Peas Educati, Inc., Publishing as Peas Addis-Wesley. Copyight 007, Peas Educati, Inc., Publishing as Peas Addis-Wesley. 5

6 10/7/014 : (How is this simila to the pevious poblems?) A paallel-plate capacito is held at a potential diffeence of 50 V. A pot is fied towad a small hole in the negative plate with a speed of 3.0 x 10 5 m/s. What is its speed when it emeges though the hole in the positive plate? (Hint: The electic potential outside of a paallel-plate capacito is zeo). Fo the situati shown in the figue, find A. The potential at points a and b.the potential diffeence between a and b. B. The potential enegy of a pot at a and b. C. The speed at point b of a pot that was moving to the ight at point a with a speed of 4.0 x 10 5 m/s. D. The speed at point a of a pot that was moving to the left at point b with a speed of 4.0 x 10 5 m/s. Copyight 007, Peas Educati, Inc., Publishing as Peas Addis-Wesley. Copyight 007, Peas Educati, Inc., Publishing as Peas Addis-Wesley. Souce chages ceate the electic potential shown. A. What is the potential at point A? At which point, A, B, o C, does the electic field have its lagest magnitude? B. Is the magnitude of the electic field at A geate than, equal to, o less than at point D? C. What is the appoximate magnitude of the electic field at point C? D. What is the appoximate diecti of the electic field at point C? Copyight 007, Peas Educati, Inc., Publishing as Peas Addis-Wesley. 6