Download PHYS 1112 In-Class Exam #2B Thu. March 18, 2010, 11:00am-12:15pm

Physics 1112
Spring 2010
University of Georgia
Instructor: HBSchüttler
PHYS 1112 In-Class Exam #2B
Thu. March 18, 2010, 11:00am-12:15pm
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 a diffraction
grating with line spacing d, with λ < d, as shown in the figure below. Assume |∆y| is the
distance (in cm) between the two 1st-order intensity maxima, observed on a screen at a
distance L on the other side of the grating. This distance |∆y| will
1st order maxima
Fig. 2.03
Δy
Screen
θ
L
Diff. Grating
Laser Beam
(A)
(B)
(C)
(D)
(E)
decrease if we increase L (keeping λ and d fixed);
decrease if we increase λ (keeping L and d fixed);
decrease if we increase 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 160N, what force would they exert on each other if r is quadrupled (×4); Q1 is
tripled with unchanged sign; and the sign of Q2 is reversed ? The two charges will
(A)
(B)
(C)
(D)
(E)
attract each other with a force of 120N
attract each other with a force of 2560N
attract each other with a force of 30N
repel each other with a force of 2560N
repel each other with a force of 30N
Problem 3: In the figure below, Q1 and Q2 are both negative point charges with |Q1 | and
|Q2 | being of comparable magnitude. Which arrow drawn at P could correctly represent the
~ generated by Q at P ?
electric field vector E
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Physics 1112
Spring 2010
University of Georgia
Instructor: HBSchüttler
Fig. 2.12
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. 2.14
------------------------E
A
B
E
+++++++++++++++++++++++++++
Assume the electron experiences a rise in electric potential, ∆V = +250V, and a loss of
potential energy, ∆U = −40aJ (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
= −25V and ∆U = −4aJ
= −50V and ∆U = −8aJ
= +50V and ∆U = +8aJ
= −250V and ∆U = −40aJ
= +250V and ∆U = +40aJ
Numerical Problems
Problem 5: If a double slit is illuminated at normal incidence by coherent (laser) light it
produces 5th order maxima at angles ±75o measured from the central (0th order) intensity
maxium. At what angles θ, measured from the central (0th order) intensity maxium, will
the 3rd order maxima be observed ?
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Physics 1112
Spring 2010
(A)
(B)
(C)
(D)
(E)
University of Georgia
Instructor: HBSchüttler
±45.0o
±22.5o
±18.8o
±70.8o
±35.4o
Problem 6: Two point charges lie on the x-axis: Q1 = −60µC is at x = 0, and Q2 is at
x = 15.0cm. A third charge q will be in equilibrium when placed at x = 10.0cm. Therefore,
Q2 is
(A)
(B)
(C)
(D)
(E)
−90µC
−15µC
+30µC
+15µC
−30µC
Problem 7: Two point charges, spaced 112.4m apart, repel each other with a force of
96.0N. What is the amount of the larger point charge if the larger charge is 2.4 times the
smaller charge?
(A)
(B)
(C)
(D)
(E)
7.5mC
13.2mC
18.0mC
22.8mC
27.6mC
Problem 8: If a charge of −360nC is uniformly spread out over a single thin, squareshaped sheet of gold foil, of 3.0m 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 foil?
~ pointing towards the foil
(A) 0.1395 × 103 N/C, E
~ pointing towards the foil
(B) 2.260 × 103 N/C, E
~ pointing towards the foil
(C) 28.76 × 103 N/C, E
~ pointing away from the foil
(D) 0.1395 × 103 N/C, E
~ pointing away from the foil
(E) 28.76 × 103 N/C, E
Problem 9: The total electric flux passing through the approximately spherical surface
of a real football (i.e., a soccer ball !!) is Φ = +452Nm2 /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
−3.20nC
+2.40nC
−1.60nC
−4.80nC
+4.00nC
Problem 10: The 900µF capacitor in a defibrillator must be charged to store ±270mC in
its two plates. What charging voltage is required for this ?
(A)
(B)
(C)
(D)
(E)
300V
400V
500V
600V
700V
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)
22.5J
81.0J
40.5J
62.5J
34.5J
Problem 12: If the electric field strength between the capacitor plates in Problem 4 is
57.0V/m, what is the magnitude and the direction of the electron’s acceleration ~a, assuming
the electron is subject only to the electric force between the plates ?
(A)
(B)
(C)
(D)
(E)
1.00 × 1013 m/s2 , ~a
1.00 × 1013 m/s2 , ~a
2.25 × 1013 m/s2 , ~a
2.25 × 1013 m/s2 , ~a
2.25 × 1013 m/s2 , ~a
pointing
pointing
pointing
pointing
pointing
leftward
downward
rightward
leftward
downward
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