Physics 202 MWF 10:20 Spring 1994 (Ford)
Final Exam
Show all your work. Partial credit will be given if earned. Write your
answers in the blanks provided.
(10 pts) 1. Point charge q1 = +1.5 × 10-6 C is on
the x-axis
at x = 1.0 m and point charge
q2 = -4.0 × 10-6 C is on the
x-axis at x = 2.0 m, as shown in the sketch.
What are the magnitude
and direction of the resultant electric field at the origin (point
P) produced by these two point charges?
Ans. magnitude _____________
direction (to the left or to the right?) _____________
(12 pts) 2. In the circuit shown in the sketch
C1 = 2.0 µF,
C2 = 6.0 µF, C3 = 3.0 µF,
and C4 = 6.0 µF. The potential
difference applied across the network is 40 V.
Calculate the charge on each
capacitor and the potential difference across each capacitor.
(1 µF = 10-6 F)
Ans. Q1 _______________
Q2 ________________
Q3 ______________
Q4 ______________
V1 _____________
V2 _____________
V3 ______________
V4 ______________
(10 pts) 3. A positive point charge
q1 = +5.0 × 10-6 C is held fixed
at the origin. A second point charge with charge q2 and mass
2.0 × 10-6 kg moves in along the x-axis toward q1.
At point a,
on the x-axis at x = 5.0 m, the charge q2 has speed 600 m/s
and at point b, on the x-axis at x = 2.0 m, the
charge q2 has
speed 400 m/s. As q2 moves between a and b the only force exerted
on it is the Coulomb force exerted by q1.
What is q2 (sign and magnitude)?
Ans. magnitude q2 = _______________
sign (+ or -?) _________________
(8 pts) 4. The circuit shown in the sketch consists of an emf, a switch,
two resistors, and a capacitor. Initially the switch is open and there is
no charge on the capacitor. At t = 0 the switch is closed.
a) Just after the switch is closed, what is
i) the current i1 through resistor R1?
Ans. _____________
ii) the current i2 through resistor R2?
Ans. ____________
iii) the potential difference vab between points a and b?
Ans. ____________
b) A long time after the switch is closed, what is
i) the current i1 through resistor R1?
Ans. _____________
ii) the current i2 through resistor R2?
Ans. ______________
iii) the potential difference vab between points a and b?
Ans. ________________
(8 pts) 5. The circuit shown in the sketch consists of an emf, a switch,
two resistors, and an inductor. Initially the switch is open and there are
no currents. At t = 0 the switch is closed.
a) Just after the switch is closed, what is
i) the current i1 through resistor R1?
Ans. ___________
ii) the current i2 through resistor R2?
Ans. ___________
iii) the potential difference vab between points a and b?
Ans. ____________
b) A long time after the switch is closed, what is
i) the current i1 through resistor R1?
Ans. _____________
ii) the current i2 through resistor R2?
Ans. _______________
iii) the potential difference vab between points a and b?
Ans. ______________
(10 pts) 6. A particle with charge q = -3 × 10-6 C is moving to the right
with speed v = 5 × 105 m/s in a region where there are
perpendicular electric and magnetic fields. The magnetic field has
magnitude 0.3 T and is directed into the plane of the paper.
a) What are the magnitude and direction (up, down, right, left) of the force
that the magnetic field exerts on the particle?
Ans. magnitude ___________
direction _______________
b) What must be the magnitude and direction (up, down,
right, left) of the electric field in the region if the
particle is to move in a straight line with constant speed through the region?
(Neglect gravity.)
Ans. magnitude _____________
direction ________________
(7 pts) 7. Coherent light of wavelength 500 nm passes through two narrow
slits A and B and an interference pattern is produced on a screen.
Point P on the screen is the location of the second
minimum above the central maximum. Let l1 be
the distance from
slit A to point P and l2 be the distance from
slit B to point P.
What is l2 - l1, the difference
between these two distances?
Ans. _______________
(10 pts) 8. Parallel rays from a very distant object are incident from the left
on the two thin lenses shown in the sketch. The converging lens has
f1 = +35 cm and the diverging lens has f2 = -20 cm. The distance between
the two lenses is 5 cm.
a) How far is the final image from the second lens?
Ans. _________________
b) Is the final image real or virtual?
Ans. _______________
(9 pts) 9. In the sketch below the rod AB makes contact with metal rails that
are 0.50 m apart. The resistance of the rail plus rod plus circuit is
5.0 
and may be considered to be constant. There is a uniform
magnetic field with magnitude B = 2.0 T and direction out of the plane
of the paper. The rod has mass 0.040 kg. The rod is pulled to the left
at constant speed v = 7.0 m/s by an external force Fext.
a) Calculate the magnitude of the induced current.
Ans. _________________
b) Is the direction of the induced current in the rod from A to B or from
B to A? (Show the direction of the induced current on the above sketch.)
Ans. ______________
c) Calculate the magnitude Fext of the external force that is
required to maintain this speed.
Ans. ______________
(9 pts) 10. Consider the fusion reaction
32He + 21H
---------> 42He + 11H
Compute the energy liberated in this reaction, in MeV.
(1 u = 1.661 × 10-27 kg. The mass of a proton is 1.007276 u, the mass
of a neutron is 1.008665 u, and the mass of an electron is 0.000549 u.)
Ans. _______________
(7 pts) 11. If two gamma-ray photons of the same energy are produced in
e+e- annihilation (the annihilation of an electron with a positron),
find the wavelength of each photon.
(The mass of an electron is 9.11 × 10-31 kg.)
Ans. _________________