Two spherical cavities, of radii a and b, are hollowed out from the interior of a (neutral) conducting sphere of radius r (fig. 2.49). at the center of each cavity a point charge is placed-call these charges qa and qb. (a) find the surface charge densities aa, ab, and ar. (b) what is the field outside the conductor? (c) what is the field within each cavity? (d) what is the force on qa and qb?

i guess it’s a and b

answer would be letter choice (a),   a ball resting on a shelf. would be another example of potential energy   >   stored energy > not moving.

a ball spinning on a finger   >   kinetic energy > moving energy

a ball rolling on the ground   >   kinetic energy   > moving energy

a   ball flying through the air   > kinetic energy   >   moving energy

hope that                                         : )

the entire statement is true and correct.  

there's no diagram, nothing is illustrated, and no question is asked.

the minimum amperage that the current in this wire would have to have so that its weight is completely supported by the magnetic force due to earth's field, assuming that no other forces except gravity act on it