Physics 224 Fall 00
Final Exam Dec
12
Good
luck! Please show all work since this will be graded with partial credit.
Problem 
Points 
Score 
Prob 
Pts 
Score 


1 
10 

9 
15 

Test 1 

2 
30 

10 
10 

Test 2 

3 
10 

11 
10 

Test 3 

4 
10 

12 
15 

Test 4 

5 
15 

13 
15 

HW/Q 

6 
10 

14 
10 

Final 

7 
10 

15 
10 

Total 

8 
10 

16 
10 

% 




Total 
200 

Grade 

Note: Homework scores
were only used if they helped the final grade.
They were not used if they lowered the grade.
_{} _{} _{}
_{}(or F/m) _{} _{}
_{} _{} _{}
_{} _{} _{}
_{} _{} DV = Ed DU = qDV _{}
V = (kQ)/R C = Q/V U = (kqQ)/r _{} _{} V = IR _{}
_{} _{} _{} _{} _{}
_{} _{} _{} _{} _{} _{}
_{} _{}Tm/A _{} _{}
1.(10pts)
The force between two positive point charges is 40N. If the charges are separated
by
a distance of 15 cm and one of the charges is 6 mC, what is the other charge?
2.(3pts
each) Circle T for True, F for False.
a) T F Charge cannot be present on an insulating
material.
b) When a current is present in a solenoid the magnetic field is found
on
the ____________ of the solenoid.
c) T F The net charge on a conductor is distributed
on the surface of the conducting material.
d) Current is defined to be the _______ ___ __________ of the charge that
flows.
e) If an electron is traveling from left to right across this page and a
magnetic field
is
projecting directly out from the page, the force acting on the electron would
point
straight _________________.
f) V = IR is the mathematical expression for _______________ law.
g) T F The force exerted by two parallel current
carrying wires is repulsive if the currents
are
in opposite directions.
h) T F Lenz’s Law states that the effect of the
induced emf is such as to oppose the change
in
flux that produces it.
i) T F Magnetic field lines start on the North pole
and end on the South pole.
j) Flux entering a closed surface is (circle one): Positive Negative
3.
(10pts) Find the sign (+/) for
DV DU DK
B· A·
E a)
A positive charge is moved from B to A
C· b) A negative charge is moved from B
to A
c) A negative charge
is moved from C to B
d)
A positive charge is moved from A to C
4.(10pts) A nonconducting uniformly charged sphere of
radius .02 meters has a total charge of
10 mC distributed throughout its volume. Find the Electric field strength at a
distance of .8 meters
from
the center of the sphere.
5.(15pts)
A point charge of 5 mC is placed at the point (2,
2) and a point charge of –5 mC is placed
at
the point (2, 0). Find the electric
field strength on a point charge placed at the point (0, 1). All
distances
are meters.
6.(10pts)
Find the potential midway between two point charges of 8 mC, and 10 mC, if they are
separated
by a distance of 2 cm.
7.(10pts)
When 9V is applied across a wire of length 1 meter and radius .1cm, a current
of .5 Amps
flows
through the wire. Find the resistivity
of the wire.
8.(10pts) The equivalent capacitance of the figure is
10mF.
What is C?
9.
(15pts) A capacitor is charged to its
maximum amount and then discharged.
Find the time elapsed when the charge on the capacitor is the same when
both charging and discharging.
10.(10pts)
A proton has a velocity of _{} m/s in a magnetic
field _{} G. Find the
force
exerted on the proton.
11.(15pts)
Four long, straight wires are at the corners of a square with sides of 20 cm as
in the diagram.
Find
the resultant magnetic field at the center of the square.
12.
(15pts) In a mass spectrometer, charged
particles enter a chamber with an electric field and
a
magnetic field present. Explain how the
particles are sorted so those only with velocity
equal
to E/B will leave the chamber. (examine
the forces on the particles and the orientation
of
the fields. also, it is ok to draw a diagram)
13.
(10pts) A parallel plate capacitor has
a capacitance of 10 mF. How could you change the
geometry
of the capacitor to double the capacitance?
14.(10pts) A square area of side 10 cm is set at a 30
degree angle to a uniform magnetic field of
.4
Tesla. Find the magnetic flux through
the area.
15.(10pts) Use the diagram to explain the direction the
current will flow as the magnet
recedes
from the loop. (invoking someone’s law would be nice.)
16.(10pts) Three ideal batteries are connected in
series with two resistors as in the diagram.
Find the
current
in the circuit.