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one is positive, the other is negative both are positive both are negative

one is positive, the other is negative both are positive both are negative both are positive or both are negative. Two charged balls are repelling each other as they hang from the ceiling. What can you say about their charges?. A) have opposite charges

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one is positive, the other is negative both are positive both are negative

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  1. one is positive, the other is negative • both are positive • both are negative • both are positive or both are negative Two charged balls are repelling each other as they hang from the ceiling. What can you say about their charges?

  2. A)have opposite charges B) have the same charge C) all have the same charge D) one ball must be neutral (no charge) From the picture, what can you conclude about the charges?

  3. A) positive B) negative C) positive or neutral D) negative or neutral A metal ball hangs from the ceiling by an insulating thread. The ball is attracted to a positive-charged rod held near the ball. The charge of the ball must be:

  4. A) 0 0 B) + – C) – + D) – – 0 0 ? ? Two neutral conductors are connected by a wire and a charged rod is brought near, butdoes not touch. The wire is taken away, and then the charged rod is removed. What are the charges on the conductors?

  5. A D B E C F Two uniformly charged spheres are firmly fastened to and electrically insulated from frictionless pucks on an air table. The charge on sphere 2 is three times the charge on sphere 1. Which force diagram correctly shows the magnitude and direction of the electrostatic forces?

  6. F2 = ? F1 = 3N Q Q F2 = ? F1 = ? 4Q Q A) 3/4 N B) 3.0 N C) 12 N D) 16 N If we increase one charge to 4Q, what is the magnitude of F1?

  7. F F Q Q ? ? Q Q d 3d A) 9 F B) 3 F C) 1/3 F D) 1/9 F The force between two charges separated by a distance d is F. If the charges are pulled apart to a distance 3d, what is the force on each charge?

  8. +4Q +Q 3R A) yes, but only if Q0 is positive B) yes, but only if Q0 is negative C) yes, independent of the sign (or value) of Q0 D) no, the net force can never be zero Two balls with charges +Q and +4Q are fixed at a separation distance of 3R. Is it possible to place another charged ball Q0 on the line between the two charges such that the net force on Q0 will be zero?

  9. – 4Q +Q 3R A) yes, but only if Q0 is positive B) yes, but only if Q0 is negative C) yes, independent of the sign (or value) of Q0 D) no, the net force can never be zero Two balls with charges +Q and –4Q are fixed at a separation distance of 3R. Is it possible to place another charged ball Q0anywhereon the line such that the net force on Q0 will be zero?

  10. e p A) it gets bigger B) it gets smaller C) it stays the same A proton and an electron are held apart a distance of 1 m and then released. As they approach each other, what happens to the force between them?

  11. +2Q A B C +4Q D d +Q d Which of the arrows best represents the direction of the net force on charge +Q due to the other two charges?

  12. A) 2 E0 B) E0 C) 1/2 E0 D) 1/4 E0 You are sitting a certain distance from a point charge, and you measure an electric field of E0. If the charge is doubled and your distance from the charge is also doubled, what is the electric field strength now?

  13. +2 +2 +1 +1 Between the red and the blue charge, which experiences the greater electric field due to the yellow charge? A) B) C) it’s the same for both +1 +1 d d

  14. +2 +2 +1 +1 Between the red and the blue charge, which experiences the greater electric force due to the yellow charge? A) B) C) it’s the same for both +1 +1 d d

  15. -2 C A Which arrow best represents the electric field at the center of the square? C B -2 C D) E = 0

  16. -Q +Q What is the direction of the electric field at the position of the X ? B C +Q A D

  17. Field Lines • Field lines point in the direction of the Coulomb force on a positive test charge due to the charge creating the field

  18. Electric fields add up vectorially

  19. Asymmetric charge distribution yields asymmetric field

  20. Parallel Plates • Constant electric field far away from the top and the bottom • Constant direction • Constant strength

  21. e p A) proton B) electron C) both the same A proton and an electron are held apart a distance of 1 m and then released. Which particle has the larger acceleration at any one moment?

  22. e p A) in the middle B) closer to the electron’s side C) closer to the proton’s side A proton and an electron are held apart a distance of 1 m and then let go. Where would they meet?

  23. Flux through an Area

  24. Curved Surface and non-uniform Field Changing for every point on surface: Strength of E Direction of E Direction of A

  25. Angle determines sign of flux

  26. What is the Flux through the Surfaces? A1 pos., A2 neg A2 pos., A1 neg Both zero None of the above

  27. A gaussian cylinder is placed in a uniform electric field of magnitude E, aligned with the cylinder axis. For each of the surfaces 1, 2, 3, is the electric flux positive, negative, or zero? 2 1 3 E

  28. A gaussian cylinder encloses a negative charge. For each of the surfaces 1, 2, 3, is the electric flux positive, negative, or zero? 2 1 3 –Q

  29. A positive charge is located outside a gaussian cylinder as shown. For each of the surfaces 1, 2, 3, is the electric flux positive, negative, or zero? +Q 2 1 3

  30. Which statement do you agree with? “Since each Gaussian surface encloses the same charge, the net flux through each should be the same.” “Gauss’s law doesn’t apply here. The electric field at the Gaussian surface in case B is weaker than in case A, because the surface is farther from the charge. Since the flux is proportional to the electric field strength, the flux must also be smaller in case B.” “I was comparing A and C. In C the charge outside the Gaussian surface changes the field over the whole surface. The areas are the same so the fluxes must be different.” None of these statements is correct. A B C -6Q +Q +Q +Q

  31. Gauss’s law problem solving Symmetry of charge distributions  Gaussian surface Draw Gaussian surface through point where you want to know E field Determine direction of E field from symmetry of charge distribution Calculate electric flux through Gaussian surface Calculate charge enclosed by surface Solve for E as a function of distance from charge using Gauss’ law

  32. What is the symmetry of a long straight wire with line charge density λ? Cylindrical Elliptical Spherical Planar

  33. What is the symmetry of a non-conducting hollow sphere with charge density ρ? Cylindrical Elliptical Spherical Planar

  34. Which Gaussian surface should we choose to calculate the electric field of a non-conducting hollow sphere with charge density ρ ? Cylinder Pillbox Sphere Other

  35. Which radius should the Gaussian sphere of a non-conducting hollow sphere with charge density ρ have? Less than inner radius of hollow sphere More than outer radius of hollow sphere Between inner and outer radius of hollow sphere Depends on where you are interested in the electric field

  36. Which is the symmetry of a sheet of metal with surface charge density σ? Cylindrical Elliptical Spherical Planar

  37. Which Gaussian surface should we choose to calculate the electric field of a metal sheet with surface charge density σ? Cylinder Pillbox Sphere Other

  38. Which of the three surfaces of the pillbox has a non-zero electric flux? Top (outside conductor) Mantle (half-submerged) Bottom All three

  39. Electric field of a solid charged sphere Choose gaussian surface A1 to calculate E field outside sphere Choose gaussian surface A2 to calculate E field inside sphere

  40. Electric field of solid charged sphere

  41. How does the electric field of a long wire depend on R? Not, Const. R 1/R 1/R2

  42. Non-conducting solid cylinder and cylindrical tube, both carry charge density 15μC/m3; R1=1/2R2=R3/3=5cm. Calculate the electric field. Group 1: inside solid cylinder Group 2: between cylinders Group 3: inside hollow cylinder Group 4: outside both cylinders

  43. Electric Field as a function of distance from axis

  44. The analogy of the potential energy of two rocks are charges between charged plates. Which plate should be on top? • Positive • Negative • Depends

  45. The analogy of the potential energy of two rocks are charges between charged plates. What does the small rock represent? • More charge • Less charge • Negative charge • Depends

  46. The analogy of the potential energy of two rocks are charges between charged plates. What is a correct analogy? • Neg. plates up and neg. charges high • Neg. plates down and neg. charges high • Pos. plates and neg. charges up/high • None of the above

  47. What is correct? • Potential would be lower at b for negative charges • The potential at b is higher for the larger charge • Negative charges go from low to high potential • None of the above

  48. + A proton is moved from position i to position f below. Is the change in its potential energy • positive, • negative, or • zero?  i  f

  49. 1. 3.  i  f  i + - - + +  i  f  f In each of the situations shown below, an electron is moved from position i to position f. Is the change in its potential energy • positive, • negative, or • zero? 2.

  50. - + Draw the field lines & equipotential lines of two charges plates

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