Physics 202 MWF 10:20 Spring 1996 (Ford)
Final Exam
Show all your work. Partial credit will be given if earned. Write your
answers in the blanks provided.
(9 pts) 1. Parallel rays from a very distant object are incident from the left
onto two thin lenses as shown in the sketch. The diverging lens has
f1 = -20 cm and the converging lens has
f2 = +35 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. _______________
(12 pts) 2.
a) Charge Q is distributed uniformly throughout an
insulating sphere of radius R. In terms of Q, what is
the electric field
(i) for r < R
Ans. ______________
(ii) for r > R
Ans. ______________
b) A solid conducting sphere of radius R has a net charge
Q. In terms of Q, what is the electric field
(i) for r < R
Ans. ______________
(ii) for r > R
Ans. _______________
NOTE: For each question, to receive credit you must give a
clear derivation of your result.
(12 pts) 3. Point charges
q1 = -5.0 × 10-6 C and
q2 = +3.0 × 10-6 C
are held fixed at the positions shown in the
sketch, on the y-axis and 0.030 m above and below the origin. Point a
is at the origin and point b is on the x-axis, 0.040 m from
the origin.
a) What is the net electric field (magnitude and direction) at the origin
(point a) produced by these two charges. (Show the direction of
E on the sketch.)
Ans. E = ____________________
direction ____________________
b) Calculate the work done by the resultant electric force of these two charges
on a third charge q3 = -4.0 × 10-6 C when
it moves from point
a to point b. Is the work done positive or negative?
Ans. W = _____________________
positive or negative? __________________
(12 pts) 4. Three capacitors are connected to an emf of 80 V, as shown in the
sketch. The capacitors have capacitances
C1 = 6.0 × 10-6 F,
C2 = 3.0 × 10-6 F, and
C3 = 5.0 × 10-6 F. After the
charges have reached their final values, calculate the magnitude of the
charge Q on each capacitor and the potential V across each
capacitor.
Q1 = ________________
V1 = ________________
Q2 = ________________
V2 = ________________
Q3 = ________________
V3 = _______________
(12 pts) 5. Consider the circuit shown in the sketch. The resistances are
R1 = 30 
and
R2 = 15 . The capacitor is
initially uncharged. The switch is closed at t = 0.
a) At some later time t, the current i1
through R1 is 9.0 A and the
current i2 through R2 is 2.0 A.
(i) What is the emf of the battery?
Ans. ______________
(ii) What is the charge q on the capacitor at this instant?
Ans. ____________
b) What are i1, i2, and q a long
time after the switch is closed?
Ans. i1 = ______________
i2 = ________________
q = __________________
(9 pts) 6. An L-C circuit consists of an inductor with
L = 0.800 H and a
capacitor with C = 6.00 × 10-4 F. The initial
charge on the capacitor
is Q and the initial current in the inductor is zero.
a) During the current oscillation, the maximum current in the inductor is
8.0 A. What was the initial charge Q on the capacitor?
Ans. ________________
b) At the instant when the current in the inductor is 4.0 A, what is the
charge on the capacitor?
Ans. _______________
(9 pts) 7. A circular loop of wire with resistance R and radius
r = 0.30 m
is in a region of uniform magnetic field. The magnetic field is directed out of
the plane of the paper and is increasing at a uniform rate of
B/t =
+0.030 T/s. The current induced in the wire
loop has magnitude 0.70 A.
a) Is the induced current clockwise or counterclockwise?
Ans. ______________
b) What is the resistance R of the loop?
Ans. __________________
(10 pts) 8. A long, straight wire carries a current I = 6.0 A in the
direction
shown in the sketch. An electron (charge
q = -1.6 × 10-19 C) is at
point P and has velocity v = 3.0 × 104 m/s in the
direction away from the wire, as shown in the sketch.
a) What is the magnetic field (magnitude and direction) at point P
due to the
current in the wire? (Show the direction of B on the sketch.)
Ans. B = _______________
direction _______________
b) What is the force (magnitude and direction) that the magnetic field of the
wire exerts on the electron when the electron is at point P?
(Show the direction of F on the sketch.)
Ans. F = _______________
direction _______________
(7 pts) 9.
a) Calculate the binding energy (in MeV) of the lithium isotope
73Li. The mass of 73Li is 7.016003 u.
Ans. ______________
b) The nucleus 23090Th undergoes alpha decay. What
are the
nucleon number A and atomic number Z of the nucleus that
is produced by this
decay?
Ans. A = _________________
Z = ______________
(8 pts) 10. When light of wavelength 400 nm is incident on a metal surface, the
maximum kinetic energy of the photoelectrons that are produced is 1.6 eV.
a) What is the maximum kinetic energy of the photoelectrons that are produced
when light of wavelength 300 nm is incident on the same surface?
Ans. ______________
b) What is the longest wavelength of light that will cause photoelectrons
to be emitted from this surface?
Ans. ______________