Download PHY 113, Summer 2007

PHY 114, Summer 2007
Langenbrunner
HW 2 – due Thursday, July 12 in class
1. What is the magnitude of a point charge whose electric field 50 cm away has a magnitude 2.0
N/C?
2. Using Gauss' Law, find the electric field inside a uniform sphere of charge Q and radius R.
Using the equation for the force on a charge in an electric field, check to make sure your answer
is consistent with the force on a charge q inside the sphere (which we found in class last week).
3. A non conducting rod of length L has charge –q uniformly distributed along its length.
a) What is the linear charge density of the rod?
b) What is the electric field at point P, a distance a from the end of the rod?
c) If P were very far away from the rod compared to L, the rod would look like a point charge.
Show that your answer to (b) reduced to the electric field of a point charge for a>>L.
-q
L
P
x
a
4. A charged cloud system produces an electric field in the air near Earth's surface. A particle of
charge -2.0 x 10-9 C is acted on by a downward electrostatic force of 3.0 x 10-6 N when placed in
this field.
a) What is the magnitude of the electric field?
b) What are the magnitude and direction of the electrostatic force exerted on a proton placed in
this field?
c) What is the gravitational force on the proton?
d) What is the ratio of the magnitude of the electrostatic force to the magnitude of the
gravitational force in this case?
5. A cube of length a holds a charge of +3C at its center.
a) What is the net flux through the cube?
b) What is the net flux through one face of the cube?