Download Conceptual Practice Problems for PHYS 1112 In-Class Exam #2A+2B

Physics 1112
Spring 2009
University of Georgia
Instructor: HBSchüttler
Conceptual Practice Problems
for
PHYS 1112 In-Class Exam #2A+2B
Thu. Mar. 19, 2009, 11:00am-12:15pm and 2:00pm-3:15pm
CP 2.01: In a two-source interference experiment two sources are oscillating in phase with
the same period. The first intensity minimum, closest to the central intensity maximum M
and to the left of M, is located at point P, as shown in Fig. 2.01. A wave crest A from source
1 and a wave trough B from source 2 arrive simultaneously at P. Therefore, A and B must
have departed from their respective sources as follows:
Fig. 2.01
P
M
Source 1
(A)
(B)
(C)
(D)
(E)
Source 2
A departed 1/2 period before B.
B departed 1/2 period before A.
A departed 1 period before B.
B departed 1 period before A.
A departed 3/2 period before B.
CP 2.01 Answer: (B)
CP 2.02: A diffaction grating is illuminated with coherent (laser) light with a wavelength
λ < d where d is the spacing between adjacent slits in the grating. The first intensity
maximum, to the right of and closest to the central intensity maximum M, is located at
point Q, as shown in Fig. 2.02. A wave crest A from slit R and a wave crest B from the
neighboring slit S to the right of R, arrive simultaneously at Q. Therefore, A and B must
have departed from their respective slits as follows:
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Physics 1112
Spring 2009
University of Georgia
Instructor: HBSchüttler
Fig. 2.02
M
Q
R S
Diff. Grating
Laser Beam
(A)
(B)
(C)
(D)
(E)
A departed 1/2 period before B.
B departed 1/2 period before A.
A departed 1 period before B.
B departed 1 period before A.
A departed 3/2 period before B.
CP 2.02 Answer: (C)
CP 2.03: A beam of coherent (laser) light of wavelength λ is incident upon a diffraction
grating with line spacing d as shown in Fig. 2.03. The distance |∆y| (in cm) between the
two 1st order intensity maxima, observed on a screen at a distance L on the other side of
the grating, will
1st order maxima
Fig. 2.03
Δy
Screen
L
Diff. Grating
Laser Beam
(A) decrease if we increase L
(B) decrease if we increase λ
2
Physics 1112
Spring 2009
University of Georgia
Instructor: HBSchüttler
(C) increase if we decrease λ
(D) increase if we increase d
(E) decrease if we increase d
CP 2.03 Answer: (E)
CP 2.04: A beam of coherent (laser) light of wavelength λ is incident upon two parallel slits
with a spacing d as shown in Fig. 2.04. The distance |∆y| (in cm) between the two adjacent
dark fringes (interference intensity minima), observed closest to the central maximum on a
screen at a distance L on the other side of the slits, will
1st dark fringes
Fig. 2.04
Δy
Screen
L
Double Slit
Laser Beam
(A)
(B)
(C)
(D)
(E)
increase if we increase L
increase if we decrease λ
decrease if we increase λ
increase if we increase d
decrease if we decrease d
CP 2.04 Answer: (A)
CP 2.05: If two 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); and q1 and q2 are
unchanged ? The two charges will
(A)
(B)
(C)
(D)
(E)
repel each other with a force of 22µN
attract each other with a force of 10N
repel each other with a force of 10N
attract each other with a force of 65000MN
repel each other with a force of 65000MN
3
Physics 1112
Spring 2009
University of Georgia
Instructor: HBSchüttler
CP 2.05 Answer: (C)
CP 2.06: If two charges q1 and q2 at some distance r attract each other with a force of 10N,
what force would they exert on each other if q1 is quadrupled (×4) and its sign is reversed;
and q2 and r are unchanged ? The two charges will
(A)
(B)
(C)
(D)
(E)
repel each other with a force of 40N
attract each other with a force of 2.1mN
repel each other with a force of 2.1mN
attract each other with a force of 56000MN
repel each other with a force of 56000MN
CP 2.06 Answer: (A)
CP 2.07: If two charges q1 and q2 at some distance r attract each other with a force of 6N,
what force would they exert on each other if q1 is doubled (×2) without changing its sign;
q2 is tripled (×3) and its sign is reversed; and r is unchanged ? The two charges will
(A)
(B)
(C)
(D)
(E)
repel each other with a force of 1N
attract each other with a force of 1N
repel each other with a force of (1/6)N
attract each other with a force of (1/6)N
repel each other with a force of 36N
CP 2.07 Answer: (E)
CP 2.08: If two charges q1 and q2 at some distance r repel each other with a force of 4.5N,
what force would they exert on each other if q1 is unchanged; q2 is doubled (×2) and its sign
is reversed; and r is tripled (×3) ? The two charges will
(A)
(B)
(C)
(D)
(E)
repel each other with a force of 1N
attract each other with a force of 1N
repel each other with a force of (1/6)N
attract each other with a force of (1/6)N
repel each other with a force of 36N
CP 2.08 Answer: (B)
CP 2.09: Q in Fig. 2.09 is positive point charge. Which arrow drawn at P could correctly
~ generated by Q at P ?
represent the electric field vector E
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Physics 1112
Spring 2009
University of Georgia
Instructor: HBSchüttler
Fig. 2.09
P
(B)
(A)
(C)
(E)
(D)
Q
(A)
(B)
(C)
CP 2.09 Answer: (A)
(D)
(E)
CP 2.10: Q in Fig. 2.10 is negative point charge. Which arrow drawn at P could correctly
~ generated by Q at P ?
represent the electric field vector E
Fig. 2.10
P
(A)
Q
(C)
(D)
(A)
(B)
(C)
CP 2.10 Answer: (C)
(B)
(E)
(D)
(E)
CP 2.11: Q1 and Q2 in Fig. 2.11 are positive point charges. Which arrow drawn at P could
~ generated by Q1 and Q2 at P ?
correctly represent the total electric field vector E
5
Physics 1112
Spring 2009
University of Georgia
Instructor: HBSchüttler
Fig. 2.11
P
Q2
(D)
(E)
(C)
(A)
(B)
Q1
(A)
(B)
(C)
CP 2.11 Answer: (E)
(D)
(E)
CP 2.12: Q1 in Fig. 2.12 is a positive point charge, and Q2 is a negative point charge.
~ generated
Which arrow drawn at P could correctly represent the total electric field vector E
by Q1 and Q2 at P ?
Fig. 2.12
P
Q2
(D)
(E)
(C)
(A)
(B)
Q1
(A)
(B)
(C)
CP 2.12 Answer: (D)
(D)
(E)
CP 2.13: In Experiment 1 a proton travels from point A to point B, in the electric field
~ generated by/between two oppositely charged capacitor plates, as shown in Fig. 2.13. In
E
Experiment 2 an electron 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.
6
Physics 1112
Spring 2009
University of Georgia
Instructor: HBSchüttler
Fig. 2.13
------------------------E
B
A
E
+++++++++++++++++++++++++++
Assume the proton experiences a drop 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 electron experience ?
(A)
(B)
(C)
(D)
(E)
∆V
∆V
∆V
∆V
∆V
= −500V and ∆U = −80aJ
= −1000V and ∆U = −160aJ
= +1000V and ∆U = +160aJ
= −1000V and ∆U = +160aJ
= −250V and ∆U = +40aJ
CP 2.13 Answer: (E)
CP 2.14: In Experiment 1 an electron travels from point A to point B, in the electric field
~ generated by/between two oppositely charged capacitor plates, as shown in Fig. 2.14. In
E
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
= +250V and ∆U = +40aJ
= −100V and ∆U = −16aJ
= +100V and ∆U = +16aJ
= −100V and ∆U = +16aJ
= −50V and ∆U = −8aJ
CP 2.14 Answer: (A)
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