SP212/3321&5521
Chapter 21 - Worksheet #1
Question 1: Two identical, electrically isolated conducting spheres A and B are separated by a
distance that is very large compared to the diameter of either sphere. Initially, sphere A has a
positive charge of +Q and sphere B has a negative charge of −2Q. Suppose that the spheres are
connected by a conducting wire (the wire is sufficiently thin such that any net charge in the wire is
negligible). What is the net charge qA and qB remaining on sphere A and sphere B after the wire is
removed?
(A) qA = −2Q and qB = +Q
(B) qA = 0 and qB = −Q
(C) qA = −Q and qB = 0
(D) qA = +Q/2 and qB = −Q/2
(E) qA = −Q/2 and qB = −Q/2
Question 2: Two point charges, with charges Q = +25 mC and q = +5.0 mC, are brought near each
other. There are no other charges nearby. How does the magnitude of the electrostatic force acting
on charge Q compare with the magnitude of the electrostatic force acting on q?
(A) The force on Q is 25 times stronger than the force on q.
(B) The force on Q is 5 times stronger than the force on q.
(C) The force on Q has the same magnitude as the force on q.
(D) The force on Q is 1/5 as strong as the force on q.
(E) We need more information to answer this question.
Question 3: Two positively charged pith balls hanging from strings repel each other due to their
charges. The first pith ball, with mass m1 and charge q1 , hangs at a 15◦ angle from the vertical
while the second pith ball, with mass m2 and charge q2 , hangs at a 30◦ angle from the vertical.
What can we say about the charges on the two pith balls?
(A) q1 is larger in magnitude than q2 .
(B) q1 is smaller in magnitude than q2 .
(C) q1 and q2 are equal in magnitude.
(D) We do not have enough information to determine which of the above is true.
30◦
15◦
m1
m2
SP212/3321&5521
Chapter 21 - Worksheet #1
Question 4: Three point charges are arranged as shown below. What is the magnitude of the net
electrostatic force acting on the middle (−3.00 nC) charge? In what direction is this force?
−3.00 nC
+1.50 nC
1.50 m
−4.50 nC
1.50 m
Question 5: A +5.0 × 10−5 C point charge is located at the origin, a −4.0 × 10−5 C point charge
is located at (0, 2.0) m, and a +3.0 × 10−5 C point charge is located at (1.0, 0) m. What is the
magnitude of the net electrostatic force acting on the charge located at the origin?
y
−4.0 × 10−5 C
2.0 m
1.0 m
+5.0 × 10−5 C
x
+3.0 × 10−5 C
SP212/3321&5521
Chapter 21 - Worksheet #1
Question 7: Three point charges are located at the corners of an equilateral triangle. Each side of
the triangle is 0.65 m long. What is the magnitude of the net electrostatic force on q1 (the −5.0 µC
charge) due to the other two charges?
q1 =−5.0 µC
5m
0.6
60◦
q2 =+2.0 µC
q3 =+2.0 µC
Question 6: Two concentric insulating hollow spheres are charged. The smaller sphere, with
radius R1 =0.18 m, has a total charge of Q1 = −2.5 µC distributed evenly across it. The
larger sphere, with radius R2 =0.54 m, has a total charge of Q2 = +4.5 µC distributed evenly
across it. A point charge, with q = +3.0 µC, is placed at a position that is r=0.36 m from the
center of the spheres. What is the magnitude of the net electrostatic force acting on the point charge?
q = +3.0 µC
r=0.36 m
R2 =0.54 m
Q1 =−2.5 µC
R1 =0.18 m
Q2 =+4.5 µC