49. At the atomic level, what is meant by saying something is electrically charged?

51. Why are objects with vast numbers of electrons normally not electrically charged?

57. An electroscope is a simple device consisting of a metal ball that is attached by a conductor to two thin leaves of metal foil protected from air disturbances in a jar, as shown. When the ball is touched by a charged body, the leaves that normally hang straight down spread apart. Why? (Electroscopes are useful not only as charge detectors but also for measuring the quantity of charge: the more charge transferred to the ball, the more the leaves diverge.)

61. How can you charge an object negatively with only the help of a positively charged object?

62. When one material is rubbed against another, electrons jump readily from one to the other but protons do not. Why? (Think in atomic terms.)

70. The proportionality constant k in Coulomb's law is huge in ordinary units, whereas the proportionality constant G in Newton's law of gravitation is tiny. What does this indicate about the relative strengths of these two forces?

72. How is the direction of an electric field indicated with electrical field lines?

82. A free electron and a free proton are placed in the same electric field. (a) How will the forces acting on them compare? (b) How will their accelerations compare? (c) How will their directions of travel compare?

85. A gravitational field vector points toward Earth; an electric field vector points toward an electron. Why do electric field vectors point away from protons?

88. If you were to expend 10 J of work to push a 1-C charge against an electric field, what would be its change of voltage?