 
Summary: Physics 208 Exam 1 Name_______________________________________________
You are graded on your work, with partial credit. See the last pages of the exam for formula sheets.
Please be clear and wellorganized, so that we can easily follow each step of your work.
1. A solid conducting sphere carrying charge Q has radius a . It is inside a concentric hollow conducting
sphere with inner radius b and outer radius c . The hollow sphere has no net charge. Use Gauss's law (and
what you know about conductors) to derive expressions for the electric field magnitude E in each of the
following regions.
You should include sketches which show the appropriate charges and appropriate Gaussian surfaces.
(a) (5) r < a:
(b) (5) a < r < b :
(c) (5) b < r < c :
(d) (5) r > c :
(e) (5) Sketch a graph of E versus r from r = 0 to r = 2c.
2. (25) A small sphere with mass 5.0 grams hangs by a thread between two parallel vertical plates 10.0 cm
apart. The plates are conducting and have uniform surface charge densities +! and !" . The charge on the
sphere is q = 2.0 !10"5
coulomb. The thread makes an angle of 30!
with respect to a vertical line.
(a) (5) Calculate the vertical component Ty of the tension in the thread.
(b) (5) Calculate the horizontal component Tx of the tension in the thread.
