Download Practice Test 2 - University of St. Thomas

Test 2 Physics 112-4 Fall 2011 p1
Practice TEST 2: coulomb’s law and gauss’
law
NAME: _____________________________________________
A solid sphere with a radius of 20 cm carries 12 μC, distributed uniformly throughout the volume. Find
the electric field strength at (a) r = 10cm, (b) r = 25 cm, and (c) r = 30cm.
Test 2 Physics 112-4 Fall 2011 p2
Show that by using a spherical surface area, Gauss’s Law can be used to recover Coulomb’s Law as long
as ε0 = 1/(4πk).
Test 2 Physics 112-4 Fall 2011 p3
An imaginary cylindrical-shaped surface that has a length equal to 20cm and a radius, R, equal to 5.00
cm, has its center at the origin and its axis along the x-axis, so that one end is at x= +7.5 cm and the
𝑁
𝑁
other is at x = -7.5cm. The electrical field is given by 𝐸⃗ = +300 𝑖̂ for x<0 and 𝐸⃗ = −100 𝑗̂ for x>0.
𝐶
𝐶
What is the net outward flux through the closed surface? What is the net charge inside the closed
surface? (Note: Watch your vector directions here!)
Test 2 Physics 112-4 Fall 2011 p4
A spherical shell 15cm in diameter carries a total charge of 54μC distributed uniformly over its surface.
A 5.0μC charge is located at x = 2.0 cm and y = 3.0 cm. What is the field strength 5.0 cm from the center
and 20 cm from the center?
Test 2 Physics 112-4 Fall 2011 p5
You are given the following configuration: a point charge q1 = +7.0 nC is at the origin and a second point
charge q2 = -6.0 nC is at x=4.0m and y=5.0. You are asked to find the electric field at y=-5.0m.
I hereby certify that all the work done on this exam is fully my own work, done without assistance and
using only the calculator and equation sheet provided.
Signature ________________________________________ Date ________
Test 2 Physics 112-4 Fall 2011 p6
Extra Credit: (+2 points) An electron is projected into a uniform electric field 𝐸⃗ = +400
initial velocity of 𝑣0 = 3.90 𝑥
𝑚
106 𝑠 𝑗̂
𝑁
𝐶
𝑖̂ with an
in the direction of the field. How far is the electron deflected
along the y-axis after traveling 1.2m in the x-direction.