Ex2_Review - Clark Musselman, Ph.D.

Spring 2015 - Physics 162 - Exam 2 Review
1. Two very large parallel sheets a distance d apart have their centers directly
opposite each other. The sheets carry equal but opposite uniform surface
charge densities. A point charge that is placed near the middle of the
sheets a distance d/2 from each of them feels an electrical force F due to
the sheets. If this charge is now moved closer to one of the sheets so that
it is a distance d/4 from that sheet, what force will feel?
(a) 4F
(b) 2F
(c) F
(d) F/2
(e) F/4
2. The figure shows four Gaussian surfaces surrounding a distribution of
(a) Which Gaussian surfaces have an electric flux of +q/✏0 through
(b) Which Gaussian surfaces have no electric flux through them?
3. A small glass bead charged to +6.0 nC is 4.0 cm from a thin, uniformly
charged, 10-cm-long glass rod. The bead is repelled from the rod with a
force of 840 mN. What is the total charge on the rod? You may assume
that the bead is closest to the midpoint of the glass rod.
4. 55.3 million excess electrons are inside a closed surface. What is the net
electric flux through the surface?
5. An electron with an initial speed of 500,000 m/s is brought to rest by an
electric field.
(a) Did the electron move into a region of higher potential or lower potential?
(b) What was the potential di↵erence that stopped the electron?
1. C
2. (a) B
(b) C
3. 4.0 ⇥ 10
4. -1.00 N m2 /C
5. (a) Hint: Positively charged particles move “properly”. Like a rock on
a hill, they would prefer to fall from higher to lower potential.
(b) -0.712 V
Full solutions are posted below.