Download PHYSICS 202 – FINAL EXAM

PHYSICS 202 – FINAL EXAM
Monday, May 7, 2007
NAME:
SECTION:
Note:
509
510
511
512
509
Recitation
Recitation
Recitation
Recitation
510
Tues
Tues
Tues
Tues
511
512
8:00
9:35
11:10
12:45
There are a total of 16 problems on this test. For each problem, write your answer in the space provided.
You may use the backs of the pages for scratch calculations if you wish, but only the work in the spaces
provided on the front of the pages will be graded.
Problems A1 through A7 are worth 4 points each. For these seven problems, you do not need to show
calculations or explain your reasoning unless requested. Also, no partial credit will be awarded for
incorrect answers.
Problems B1-B9 are worth 8 points each. For these nine problems, you must show your work and/or
explain your reasoning to receive any credit for a problem. Merely stating the answer is NOT sufficient.
Partial credit will be awarded where appropriate. Also, to receive full credit in this part:
• Numerical answers should be given with 3 significant figures and be correct to within 2%.
• An answer can not be completely correct if it has the wrong units!
GOOD
LUCK
!!!!!
Additional information not on the standard Final Exam equation sheet:
NA = 6.022 x 1023 molecules/mole
14
C T1/2 = 5730 yr
In living tissue: 0.255 Bq/(gm C)
Section A: Encircle the correct answer(s). Note that there may be more than one correct answer to a
question. No partial credit will be awarded.
A1: The figure shows a gold leaf electroscope. It consists of a metal tube with a metal ball at the top and
a sheet of extremely thin gold leaf at the other end. The gold leaf is fastened in such a way that it is
free to pivot about its upper edge. Assume the gold leaf hangs straight downward prior to the
experiment in part (a).
(a) (2 points) If you bring a charged rod close to the metal ball at the
top without touching it, the gold leaf:
Pivots outward
Hangs straight downward
(b) (2 points) Now you touch the charged rod to the metal ball for a
second or so. After you then remove the charged rod, the gold leaf:
Pivots outward
A2:
Hangs straight downward
The two coils shown in the figure are parallel to each other and are
connected to batteries. Coil A is held in place. Coil C is free to move.
After the switch S is closed, Coil C will initially move:
Toward Coil A
Away from Coil A
Into the paper
Out of the paper
Upward
Downward
A3: A square loop of wire is pulled upward out of the space between the poles of
a magnet, as shown in the figure. As this is done, the current induced in this
loop, as viewed from the N pole of the magnet, will be directed:
Clockwise
Counterclockwise
Zero
A4: A series R-L-C circuit is powered by an ac sinusoidal voltage source. Encircle the phase diagram
that illustrates the relationship between the current i and the potential drop vC across the capacitor:
A5: An object lies outside the focal point of a converging lens. Which of the following statements about
the image formed by this lens must be true?
(a) The image is always real and inverted.
(b) The image could be real or virtual, depending on how far the object is past the focal point.
(c) The image could be erect or inverted, depending on how far the object is past the focal point.
(d) The image is always on the opposite side of the lens from the object.
A6: Laser light of wavelength λ passes through a thin slit of thickness a and produces its first dark
fringes at angles of ±450 with the original direction of the beam. The slit is then replaced by a circle
of diameter a. When the same laser light is passed through the circle, the first dark fringe occurs at
±59.60
±54.90
±36.90
±35.40
A7: Suppose that a person who has one hand in a uniform beam of x rays receives a dose of 90 millirem
(mrem) in 30 s. This person now puts both hands side by side in the beam for 30 s. Assuming the
beam is wide enough to cover both hands equally, the radiation dose that she will receive during the
second 30 s period is:
180 mrem
90 mrem
45 mrem
Can’t tell
Section B: Must show your work. Partial credit will be awarded where appropriate.
B1: A point charge of -5.00 nC is at the origin, and a second point charge of +7.00 nC is on the x axis at x
= 0.800 m. Find the magnitude and direction of the electric field at the point x = 30.0 cm on the x
axis.
Direction:
+x
-x
Magnitude ________________________________
+y
-y
B2: A point charge Q = +4.80 μC is held fixed at the origin. A second point charge q = +1.40 μC with
mass of 2.80 x 10-4 kg is placed on the x axis, 0.250 m from the origin. (a) What is the electric
potential energy U of the pair of charges? (Take U to be zero when the charges have infinite
separation.) (b) The second point charge is released from rest. What is its speed when its distance
from the origin is 1.00 m?
Potential energy __________________________
Speed __________________________________
B3: A circular coil of wire with average radius 0.0630 m and 30 turns lies in the plane of the paper. It
carries a current of 6.00 A in a counterclockwise sense. The coil is in a uniform 1.20 T magnetic
field directed toward the right. Find the magnetic moment of the coil and the torque on the coil.
Magnetic moment ____________________________________
Torque ___________________________________
B4: An inductor used in a dc power supply has an inductance of 8.00 H and a resistance of 180 Ω and
carries a current of 0.450 A. (a) How much energy is stored in the inductor? (b) At what rate is
thermal energy developed in the inductor? (c) From your answers to parts (a) and (b), what can you
say about the change in the magnetic field energy with time?
Stored energy ____________________________________________
Rate of thermal energy _____________________________________
Magnetic energy is:
Increasing
Decreasing
Can’t tell
B5: We can reasonably model a 40 W incandescent lightbulb as a sphere 6.0 cm in diameter.
Typically, only about 3% of the energy goes to visible light; the rest goes largely to
nonvisible infrared radiation. What is the visible light intensity in W/m2 at the surface of the
bulb? What are the amplitudes of the electric and magnetic fields of the visible light at this
surface?
Light intensity _______________________________________
Electric field amplitude ________________________________
Magnetic field amplitude _______________________________
B6: You have a microscope that is 20.0 cm long between the objective and eyepiece lenses. The
objective lens has a focal length of 9.00 mm. The microscope forms its final image at infinity. What
should be the focal length of the eyepiece lens for this microscope to have an overall magnification
of 150x?
Focal length ___________________________________
B7: Rumor has it that the US military has spy satellites in orbit carrying telescopes that can resolve
objects on the ground as small as 15.0 cm. If we assume that such satellites orbit about 400 km
above the ground and that they focus light of wavelength 500 nm, what would have to be the
minimum diameter of the mirror (or objective lens)?
Diameter _________________________________
B8: The photoelectric work function of potassium is 2.3 eV. If light having a wavelength of 220 nm falls
on potassium, find the stopping potential (in volts), the kinetic energy (in electron volts) of the most
energetic electrons ejected, and the maximum speed of the ejected electrons.
Stopping potential ______________________________
Kinetic energy _________________________________
Speed ________________________________________
B9: A sample of charcoal from an archaeological site contains 55.0 gm of carbon and decays at a rate of
0.778 Bq. How old is it?
Age ________________________________________