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Unformatted text preview: Physics 272— Practice Final Exam
Spring 2010
Prof. Mohan Kalelkar Your name sticker with exam code . The exam will last from 1:00pm to 3:00pm. Use a # 2 pencil to make
entries on the answer sheet. Enter the following id information now,
before the exam starts. . In the section labelled NAME, enter your last name, then ﬁll in the
empty circle for a blank, then enter your ﬁrst name, another blank,
and ﬁnally your middle initial. . Under STUDENT # enter your 9~digit Student ID Number. Under
COURSE enter 272. Under CODE enter the exam code given above. . During the exam, you may use pencils, a calculator, and ONE 831,” x 11” sheet of paper with formulas and notes. . There are 24 multiplechoice questions on the exam. For each ques
tion, mark only one answer on the answer sheet. There is no subtrac
tion of points for an incorrect answer, so even if you cannot work out
the answer to a question, you should make an educated guess. At the
end of the exam, hand in only the answer sheet. Retain this question
paper for future reference and study. . Useful numerical constants are given on the next page. Before starting
the exam, make sure that your copy contains the page of constants
and all 24 questions. Bring your exam to the proctor if this is not the
case. Acceleration due to gravity 9 = 9.8 m/s2
Elementary charge 6 = 1.6 x 10“19 C' Proton charge = 1.6 x 10“19 0 Electron charge = —1.6 x 10“19 C' 1 electron volt (eV) = 1.6 x 10"19 J Proton mass = 1.673 X 10’27 leg = 938.3 Jl/IeV/c2
Electron mass = 9.11 X 10’31 kg = 0.511 MeV/cz
1/47r50 = 9 x 109 N  mZ/C'2 110 = 4m ><10’7 T~m/A Index of refraction of air = 1.00 Powers of ten: m1cro(
10 1(5f)1()—(12>)1()_(9n10.6 10£m centi(c kilo(k Mega(M G1ga(G Tera(T
10—(2)10+3> 10+6)1)0+910+12) A proton (charge = +6; mass = M) and a deuteron (charge = +6; mass =
2M) enter the same magnetic ﬁeld, and both move in circular paths. The
radius of the proton’s path is twice that of the deuteron’s. It follows that
the proton’s kinetic energy is ) twice that of the deuteron’s ) half that of the deuteron’s ) eight times that of the deuteron’s
) four times that of the deuteron’s
) onequarter of the deuteron’s a
b
c
d
e See the ﬁgure for this question. At a: = O a long straight wire carries current
I INTO the plane of the paper. At a: = D, another long straight wire carries
current 2] INTO the plane of the paper. What is the direction of the force
on the wire at the origin? 9, a) Towards the positive X—direction b) Towards the positive y—direction
c) Out of the plane of the paper d) Towards the negative Xdirection
e) None of the other answers In the preceding problem, at what point on the X—axis is the net magnetic
ﬁeld due to the two wires equal to zero? (Exclude points at inﬁnity from
consideration). a) 22D b) :232D/2
c) a: =D/3
d) a: = —D
e) at: ~2D See the ﬁgure for this question. A segment of a wire is in the shape of an
arc of a circle of radius R, and carries current I in the direction shown. The
arc subtends a 45° angle. What is the contribution to the magnetic ﬁeld at
the center 0 by the current in the arc? MOI/4R out of the paper /7 a)
b) ,LLOI / 4R into the paper Y\ / "
c) MOI/2R into the paper / /
d) MOI/16R into the paper / / o
e) MOI/16R out of the paper C: K) H“?
\
\
\ 5. See the ﬁgure for this question. A rectangular loop of wire of dimensions
a and b is being pulled with speed 2) out of a uniform magnetic ﬁeld B
directed into the paper. If the loop has a resistance R, what is the induced
current in it, when it is partially outg) of the ﬁeld as shown in the @ﬁgure? a) B cw / R clockwise b) Bbv/R clockwise
d) 3610/ R counterclockwise @ g ”,6"
) e Bbv/R counterclockwise
121 a? 6. See the ﬁgure for this question. Two concentric circular loops of wire lie in
the plane of the paper. The outer loop carries a current I. Which of the
following is true? 0 I: If I is counterclockwise and constant, the induced current in the
inner loop will be nonzero and clockwise. a II: If I is counterclockwise and increasing, the induced current in the
inner loop will be nonzero and counterclockwise. 0 III: If I is clockwise and decreasing, the induced current in the inner
loop will be nonzero and clockwise. I and II are true; III is false
II and III are true; I is false
I and III are true; II is false
Only III is true Only I is true CL 0 U“ 99
VVVVV CD 7. If the current through an inductor is INCREASING, which of the following
statements will be true? a) The self~induced emf is zero b) The energy in the inductor remains constant
c) The inductance of the inductor is decreasing
d) The inductance of the inductor is increasing
e) None of the other staements are true 10. 11. An ideal transformer has 200 primary turns and 50 secondary turns. If 400
volts (rms) is placed across the primary, what is the current (rms) in the
secondary if the total resistance in the secondary circuit is 5 Q? a) None of the other answers ‘ b) 80 A
c) 20 A
d) Zero
e) 320 A Which of the following statements are true? 0 I: Electric utilities use a transformer to step up the voltage before
transmission, so as to reduce power losses during transmission. 0 II: Transformers work equally well with DC input as with AC. 0 III: A stepup transformer increases both the voltage and the current. I and II are true; III is not
Only I is true I and III are true; II is not
Only II is true None of the statements are true D. o U‘ 93
VVVVV CD An electromagnetic wave is traveling along the +j direction. Its associated
magnetic ﬁeld is along the —z' direction at one instant. What is the direction
of the associated electric field at that instant? a) +71 13) ”j
c) +k
d) '
6) —2
None of the other answers An astronaut of the future steps out of her spaceship into interstellar space.
She fires a laser that provides 109 W of power continuously for one minute!
If the total mass of the astronaut and her equipment is 100 kg, how far
does she move in that minute, assuming she started from rest? a) More than 100 m b) Less than 4 m c) Between 40 and 100 m
d) Between 4 and 10 m
e) Between 10 and 40 m 12. 13. 14. 15. A 100 W light bulb is radiating light in all directions. A panel of area 0.01
m2 is located 5 m from the bulb, and the light hits it perpendicularly. What
is the radiation force on the panel, assuming that it completely absorbs the
light hitting it? ) About 3.3 x 10'7 N
) About 1.1 X 10'11 N
) About 3.3 X 10'9 N
) About 1.1 x 108 N
) About 3.3 X 10'10 N a
b
c
d
e A ray of light goes from air into water. Which of the following is true? ) Its wavelength decreases ) Its frequency increases ) Its speed stays the same ) Its wavelength stays the same
) Its frequency decreases a
b
c
d
' 6
See the ﬁgure for this question. A ray of light goes from air into a flat block \
of glass (index of refraction = 1.5) at an angle of 360 with the normal to the interface. After passing through the glass, at what angle to the normal
will the ray emerge into air? ’ a) 620
b) 23°
c) 67°
d) 360
e) The ray won’t emerge into air, because it will be totally internally ‘ reﬂected in the glass A ﬁsh looking up at the water surface sees a circular hole surrounded by a
mirror. How far below the water surface is the ﬁsh, if the radius of the hole is 2.1 m and the index of refraction of water is 1.33? a) About 1.8 m
b) About 2.8 m
c) About 2.4 m
d) About 1.6 m
e) About 2.1 m 16. 17. 18. 19. An object is placed a distance 19 in front of a concave mirror of focal length
+3 cm. The image is on the same side of the mirror as the object, and
lies 8 cm closer to the mirror than the object, i.e. the distance between the
object and the image is 8 cm. In which of the following ranges does the
value of 1? lie? a) 8<p£110m
b) 11<p§14cm
c) 14<p_<_17cm
d) 17<p§20cm
) e p>200m A convex mirror has a focal length f < 0. Which of the following statements
about the image of a real object are true? a I: The image must necessarily be virtual
a II: The image must necessarily be upright 0 III: The image must necessarily be smaller than the object All three statements are false
All three statements are true
I and II are true; III is false
III is true; I and II are false
II and III are true; I is false :1. a U‘ 93
vvvvv (D An object is placed 3 cm from a lens. the image is found to lie 12 cm from
the lens, on the same side as the object. What is the focal length f of the
lens, and is the image upright or inverted? a) f = +2.4 cm; upright image b) f 2 ~40 cm; upright image c) f = +4.0 cm; upright image d) f — +2.4 cm; inverted image
) f e = ——2.4 cm; inverted image See the ﬁgure for this question. Three lenses are shown. thih ones are
converging (f > 0) and which are diverging (f < 0)? a) All three are diverging I "T!“
b II is converging; I and III are diverging )
c) I is converging; II and III are diverging
d) I and II are converging; III is diverging
) e I and III are converging; II is diverging 20. 21. 22. 23. A diverging lens of focal length ~10 cm is placed 10 cm to the right of an
object. Another 10 cm to the right of this lens is placed another diverging
lens, also of focal ~10 cm. Where does the ﬁnal image lie? ) 30 cm to the right of the second lens
) 3.3 cm to the left of the second lens
) 10 cm to the right of the second lens
) 6.0 cm to the left of the second lens
) 30 cm to the left of the second lens a
b
c
d
e
A nearsighted person is one who cannot see objects clearly beyond a certain
distance. A farsighted person is one who cannot see objects clearly that are closer than a certain distance. What kinds of spectacles would correct these
defects? a) Nearsighted: diverging lens; Farsighted: converging lens
b) Nearsighted: converging lens; Farsighted: diverging lens
c) Nearsighted: converging lens; Farsighted: either kind d) Both should use converging lenses e) Both should use diverging lenses A double—slit experiment uses a slit spacing d and light of wavelength A. On
a screen located a long distance L away (L >> d), the interference pattern
shows that adjacent bright fringes are separated by a small distance y. If
the slit spacing is then doubled, what will be the new separation between
adjacent bright fringes? 84) 4y
b) 21/2
C) 21/4
d) y e) 2y A diffraction grating of total width 4 cm is illuminated by light of wave—
length 577 nm. The second—order (m = 2) maximum is formed at an angle
of 41.25°. What is the total number of slits (rulings) in the grating? a) About 12000
b) About 23000
c) About 5000
d)
6) About 19000
About 8000 24. A circular radar antenna on a navy ship radiates and receives electromag—
netic waves of 0.02 m wavelength to detect two small boats located 9 km
from the ship. If the small boats are 100 m apart from each other, what
must be the minimum diameter of the antenna so that the boats can be
distinguished as two objects? a) About 0.45 m
b) About 0.27 m
c) About 1.1 m
d) About 1.4 m
6) About 2.2 m ...
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 Spring '10
 Brahmia
 Physics

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