Download PHYS 1112 In-Class Exam #2A Thu. March 18, 2010, 9:30am-10:45am

Physics 1112
Spring 2010
University of Georgia
Instructor: HBSchüttler
PHYS 1112 In-Class Exam #2A
Thu. March 18, 2010, 9:30am-10:45am
This is a closed-book, closed-notes exam, but you are permitted to bring and use a copy
of the official Formula Sheet for this exam, which you should have printed out from the
PHYS1112 web page.
The exam consists of 12 multiple-choice questions. Each question is worth one raw score
point. There will be no penalty for wrong answers. No partial credit will be given. I
recommend that you read all the questions at the start so that you can allocate your time
wisely. (Answer the easy questions first!)
You may use a scientific calculator for arithmetic only; your calculator must be non-graphing,
non-programmable, and non-algebraic. You are not allowed to share your calculator. The
use of cell phones, pagers, PDAs, or any other electronic devices (besides calculators) is
forbidden. All such gadgets must be turned off and put away; distractions caused by these
devices will not be tolerated.
• Do not open the exam until you are told to begin.
• Make sure the scantron sheet has your name and your UGA Card ID (810-...) number
filled in. Make sure you also have entered your name, UGA Card ID number and
signature on the exam cover page (this page!) below.
• At the end of the exam period you must hand in both your scantron sheet and this
exam cover page, signed and with your name and UGA Card ID (810-...) number
filled-in. You may keep all other pages (pages 3+) of this exam paper.
• Your exam will not be graded, and you will receive a score of zero, if you do not hand
in both a properly filled in scantron sheet and this properly filled-in and signed exam
cover page.
• You have until the end of the class period (i.e. until 10:45am for Period 2 Class, until
12:15pm for Period 3 Class) to finish the exam and hand in the required exam materials
described above.
By signing below, you indicate that you understand the instructions for this exam and agree
to abide by them. You also certify that you will personally uphold the university standards
of academic honesty for this exam, and will not tolerate any violations of these standards by
others. Unsigned exams will not be graded.
Name (please print):
UGACard ID (810-...) #:
Signature:
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Physics 1112
Spring 2010
University of Georgia
Instructor: HBSchüttler
WORKSPACE
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Physics 1112
Spring 2010
University of Georgia
Instructor: HBSchüttler
Conceptual Problems
Problem 1: A beam of coherent (laser) light of wavelength λ is incident upon two parallel
slits with spacing d, and with λ < d, as shown in the figure below. Assume |∆y| is the
distance (in cm) between the two dark fringes (interference intensity minima), observed
closest to the central maximum on a screen at a distance L on the other side of the doubleslits. This distance |∆y| will
1st dark fringes
Fig. 2.04
Δy
Screen
θ
L
Double Slit
Laser Beam
(A)
(B)
(C)
(D)
(E)
decrease if we decrease L (keeping λ and d fixed);
decrease if we increase λ (keeping L and d fixed);
decrease if we decrease d (keeping λ and L fixed);
increase if we decrease λ (keeping L and d fixed);
increase if we increase d (keeping λ and L fixed).
Problem 2: If two point charges Q1 and Q2 at some distance r repel each other with
a force of 10µN, what force would they exert on each other if Q1 is tripled (×3) without
change of sign; r is doubled (×2), and the sign of Q2 is reversed ? The two charges will
(A)
(B)
(C)
(D)
(E)
attract each other with a force of 13.33µN
attract each other with a force of 15µN
repel each other with a force of 15µN
repel each other with a force of 7.5µN
attract each other with a force of 7.5µN
Problem 3: In the figure below Q1 is a positive and Q2 is a negative point charge, |Q1 |
and |Q2 | being of comparable magnitude. Which arrow drawn at P could correctly represent
~ generated by Q1 and Q2 at P ?
the electric field vector E
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Physics 1112
Spring 2010
University of Georgia
Instructor: HBSchüttler
Fig. 2.11
P
(D)
Q2
(E)
(C)
(A)
(B)
Q1
(A)
(B)
(C)
(D)
(E)
Problem 4: In Experiment 1 an electron travels from point A to point B, in the electric
~ generated by/between two oppositely charged capacitor plates, as shown in the figure
field E
below. In Experiment 2 a proton travels from point A to point B, in the same electric field
between the same two charged capacitor plates. A proton has a charge +e and an electron
has a charge −e.
Fig. 2.13
------------------------E
B
A
E
+++++++++++++++++++++++++++
Assume the electron experiences a drop in electric potential, ∆V = −1500V, and a gain of
potential energy, ∆U = +240aJ (where 1aJ ≡ 10−18 J), in traveling from A to B. What will
the proton experience ?
(A)
(B)
(C)
(D)
(E)
∆V
∆V
∆V
∆V
∆V
= −50V and ∆U = −8aJ
= −100V and ∆U = −16aJ
= +100V and ∆U = +16aJ
= −1500V and ∆U = −240aJ
= +1500V and ∆U = +240aJ
Numerical Problems
Problem 5: If a diffraction grating is illuminated at normal incidence by coherent (laser)
light it produces 3rd order maxima at angles of ±72.0o measured from the central (0th
order) intensity maxium. At what angles θ, measured from the central (0th order) intensity
maxium, will the 2nd order maxima be observed ?
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Physics 1112
Spring 2010
(A)
(B)
(C)
(D)
(E)
University of Georgia
Instructor: HBSchüttler
±24.0o
±15.2o
±48.0o
±18.5o
±39.3o
Problem 6: Two point charges lie on the x-axis: Q1 = +360µC is at x = 0, and Q2 is at
x = 10.0cm. A third charge q will be in equilibrium when placed at x = 12.0cm. Therefore,
Q2 is
(A)
(B)
(C)
(D)
(E)
+60µC
+10µC
−60µC
−10µC
−30µC
Problem 7: Two point charges, spaced 112.4m apart, repel each other with a force of
140.0N. What is the amount of the smaller point charge if the larger charge is 3.5 times the
smaller charge?
(A)
(B)
(C)
(D)
(E)
3.5mC
5.5mC
7.5mC
9.5mC
26.3mC
Problem 8: If a charge of +72µC is uniformly spread out over a single, very thin square
of titanium sheet metal, of 4.0m sidelength, what is the strength and the direction of the
electric field generated by that charge, very close to the surface and far from the edges of
that sheet?
~ pointing away from the sheet
(A) 9904. × 103 N/C, E
~ pointing away from the sheet
(B) 254.2 × 103 N/C, E
~ pointing away from the sheet
(C) 40.46 × 103 N/C, E
~ pointing towards the sheet
(D) 9904. × 103 N/C, E
~ pointing towards the sheet
(E) 40.46 × 103 N/C, E
Problem 9: The total electric flux passing through the approximately spherical surface
of a real, NBA-approved basket ball is Φ = −113Nm2 /C (assuming outward directed
normal to the surface). What is the total electric charge enclosed inside the ball ?
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Physics 1112
Spring 2010
(A)
(B)
(C)
(D)
(E)
University of Georgia
Instructor: HBSchüttler
−1.00nC
−0.60nC
+0.80nC
+0.40nC
+2.20nC
Problem 10: The 1500µF capacitor in a defibrillator is charged with a 200V battery.
What is the charge stored on the positive plate of this capacitor ?
(A)
(B)
(C)
(D)
(E)
100mC
300mC
500mC
700mC
900mC
Problem 11: How much electric field energy is stored in the defibrillator capacitor in
Problem 10 when it is fully charged ?
(A)
(B)
(C)
(D)
(E)
20J
90J
60J
80J
30J
Problem 12: If the electric field strength between the capacitor plates in Problem 4 is
2610.V/m, what is the magnitude and the direction of the proton’s acceleration ~a, assuming
the proton is subject only to the electric force between the plates ?
(A)
(B)
(C)
(D)
(E)
25.0 × 1010 m/s2 , ~a
25.0 × 1010 m/s2 , ~a
60.0 × 1010 m/s2 , ~a
60.0 × 1010 m/s2 , ~a
60.0 × 1010 m/s2 , ~a
pointing
pointing
pointing
pointing
pointing
rightward
upward
leftward
upward
rightward
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