Choose the one alternative that best completes the statement or answers the question.
1) A point charge
800 nC and two unknown point charges,
, are placed as shown. The
electric field at the origin
, due to charges
, is equal to zero. In Fig. 21.1a, the number
of excess electrons in charge
is closest to:
2) Which of the following statements about electric field lines due to a charge arrangement are
correct? (There may be more than one correct choice.)
A) Charges must move along these field lines.
B) They can never cross.
C) If the electric force on an electron points upward at a point, the direction of the electric field is
downward at that point.
D) They point away from negative charges.
E) The more closely the lines are spaced, the stronger the electric field.
3) Two uncharged metal spheres, #1 and #2, are mounted on insulating support rods. A third metal
sphere, carrying a positive charge, is then placed near #2. Now a copper wire is momentarily
connected between #1 and #2 and then removed. Finally, sphere #3 is removed. In this final state
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