What is interesting about this result? We solved in terms of the charge density σ on the conductor. If we
solve instead in terms of Q , the total charge on the conductor, we recover the formula for the electric
field of a point charge:
Practice Problems
Multiple Choice:
Questions 1 and 2
Two identical positive charges Q are separated by a distance a , as shown above.
1 . What is the electric field at a point halfway between the two charges?(A) kQ /a 2
(B) 2kQ /a 2
(C) zero
(D) kQQ /a 2
(E) 2kQ /a
2 . What is the electric potential at a point halfway between the two charges?
(A) kQ /a
(B) 2kQ /a
(C) zero
(D) 4kQ /a
(E) 8kQ /aQuestions 3 and 4
The diagram above shows two parallel metal plates that are separated by distance d . The potential