Phy 214 Test 1 11 pts each 1
point free!
Spring 2005
1. You have three metal blocks marked A, B, and C,
sitting on insulating stands. Block A is charged "+" but blocks B and
C are neutral.
Without using any additional equipment,
and without altering the amount of charge on block A,
explain how you could make block B be
charged "+" and block C be charged "-". Explain your
procedure in detail, including diagrams of
the charge distributions at each step in the process.
2. In the diagram below, draw a vector showing the force
vector on each of the charged objects caused by the other charged object. Make the lengths of the vectors
indicate the magnitude of the forces.
3. Draw on the plastic sheet showing the polarization of
the molecules in the plastic sheet caused by the charged rod. Be very specific .
4. These two
solid spheres initially have the charge evenly distributed on their
surfaces.
a.
If an electron were to be placed at position A, what
would be the magnitude and direction of the net force acting on it due to the
two charged spheres?
b.
If an electron were to be placed at position B, what
would be the magnitude and direction of the net force acting on it due to the
two charged spheres?
c.
If an electron were to be placed at position C, what
would be the magnitude and direction of the net force acting on it due to the
two charged spheres?
5. The charges in the diagram below are
located on the corners of a square that is 6 m on each side. Find the magnitude and direction of the
electric field at P.
6.
An electric field of
magnitude 500 N/C is directed
northward in a particular location.
Determine the magnitude and direction of the acceleration of
an electron placed at this location. (mass of an electron is 9x10
-31 kg, charge is 1.6x10-19C.)
7.
Two very thin plastic sheets are close to each other and carry
equal and opposite uniform charge distributions. Explain briefly why the field between the sheets is much
larger than the field outside.
Illustrate your argument on a diagram
8.
You are the captain of a spaceship. You need to measure the electric
field in space in the vicinity of the spaceship. You send a crew member outside with a meter stick, a
stopwatch, and a small ball (of known mass M and net charge +Q (held by insulating strings while being carried). You must
explain to the crew member what observations of the ball to make for you, and
explain how you will use those observations to determine the magnitude and
direction of the electric field at location P.
a) Write down the instructions (in step by step form) you
will give to the crew member.
b) Explain how you will analyze the data that the crew
member brings you, to determine the magnitude and direction of the electric
field at location P. Give the
formula you will use to obtain the Electric field E in terms of the data
obtained.
9. Consider a thin plastic rod as
indicated in the figure below. The rod carries a uniformly distributed
positive charge 5C. Follow
the steps below to obtain the magnitude and direction of the electric field E
at the point P,due to the rod.
a)
Use a diagram to explain how you plan to cut up the charged rod, and
draw the DE contributed by a representative piece.
b)
Express algebraically the contribution this representative piece makes
to the electric field at P. Be
sure to show your incremental component dE of the electric field on your
drawing.
c)
Write the summation as an integral for E, and simplify the integral as
much as possible. Be sure to show
the boundaries on the integral
d)
Evaluate the integral to find the magnitude of E.
