Download Phys214 Final Exam

Phys214 Final Exam
(30 problems. 10 points each. Total 300 points)
1. A woman 1.6 m in height wants a plane mirror so that she can view her full height. The
minimum vertical size of such a mirror is
A. 0.4 m.
B. 0.8 m.
C. 1.6 m.
D. 3.2 m.
E. impossible to say without knowing the viewing distance.
2. The speed of light in a certain type of glass is 40% slower than the speed of light in air. The
index of refraction for that type of plastic is about
A. 1.33.
B. 1.4.
C. 1.5.
D. 1.67.
3. What’s the voltage difference across the 25-Ω resistance?
A.
B.
C.
D.
E.
0.5 V
1.2 V
2.5 V
25 V
30 V
4. A power rating printed on a lightbulb assumes a voltage of 120 V is applied to the bulb. If
two 100 W bulbs are connected in series to a 120 V source,
A. each bulb radiates less than 100 W.
B. each bulb radiates 100 W.
C. each bulb radiates more than 100 W.
D. no current will pass through the bulbs.
5. Two 10- light bulbs are connected in parallel to one another, and this combination is
connected to a 6-V battery. What is the total current flowing around the loop?
A.
B.
C.
D.
E.
2.4 A
1.2 A
12 A
0.5 A
15 A
6. What is the power provided by two 1.5-V batteries in series to a 20- light bulb in the same
circuit?
A.
B.
C.
D.
E.
0.95W
0.45 W
45 W
2.3 W
4.5 W
7. The daytime sky is blue, on sunny days, because the atmosphere
A. is most efficient at scattering red light.
B. absorbs blue light.
C. is more efficient at scattering blue light.
D. absorbs the red light.
E. contains small amounts of water vapor that give the air its blue color.
8. On a day when the speed of sound in air is 340 m/s, a lightning bolt is observed and the
resultant thunderclap is heard 2 seconds afterwards. About how far away was the lightning
bolt?
A. 170 m.
B. 680 m.
C. 1020 m.
D. 1700 m.
9. Small metal ball has charge q = +0.05C and mass, m = 0.025kg. The ball enters a region of
magnetic field B = 0.5 T that is perpendicular to its velocity v = 200m/s. What is radius of
the curve ball will move through in magnetic field?
A.
B.
C.
D.
E.
200m
100m
250m
120m
50m
10. A coil of wire with 50 turns has a uniform magnetic field of 0.4 T passing through the coil
perpendicular to its plane. The coil encloses an area of 0.03 m2. If the flux through the coil
is reduced to zero by removing it from the field in a time of 0.25 s, what is the induced
voltage in the coil?
A.
B.
C.
D.
E.
0.012 V
0.12 V
0.60 V
1.5 V
2.4 V
11. The magnetic field point into the page and is increasing, what’s the direction of the induced
currents in the closed circular loop?
A. Clockwise
B. Counterclockwise
C. No induced currents.
12. Consider two different samples of radioactive isotopes, one naturally occurring and the other
artificially produced. If the samples have the same number of nuclei, then
A. the one with the shorter half-life is likely more dangerous.
B. the one with the smaller atomic mass is likely more dangerous.
C. the artificially produced one is likely more dangerous.
D. they are equally dangerous.
13. A guitar string has a mass of 4 g, a length of 74 cm, and a tension of 400 N. These values produce a
wave speed of 274 m/s. What is the frequency of the second harmonic?
A.
B.
C.
D.
E.
92.5 Hz
123 Hz
185 Hz
370 Hz
740 Hz
14. What is the wavelength of the photon emitted in the transition from n = 4 to n = 2? Note: h = 6.626 x
10-34 J s. 1µm = 10-6 m
A.
B.
C.
D.
E.
0.96 µm
0.400 µm
12 µm
0.487 µm
20 µm
15. Plutonium-239 is a radioactive isotope of plutonium produced in nuclear reactors.
Plutonium has an atomic number of 94. How many protons and how many neutrons are in the
nucleus of this isotope?
A.
B.
C.
D.
E.
94 protons, 94 neutrons
145 protons, 94 neutrons
94 protons, 145 neutrons
94 protons, 239 neutrons
239 protons, 94 neutrons
16. If we start with 193986560 atoms of a radioactive substance with a half-life of 3 hours, how many
atoms of that element remain after 60 hours?
A.
B.
C.
D.
E.
10000
185
2000
315
505
17. When antimatter is mixed with matter, they annihilate to energy according to E = mc2. Assuming 0.5
kg of antimatter mix with 0.5 kg of matter. What’s the approximate total amount of energy is released
in kilotons of TNT? (Note: 20
= 8.4 × 10 . )
A. 2000 kilotons
B. 40 kilotons
C. 21000 kilotons
D. 0.5 kilotons
E. 0.005 kilotons.
18. Unpolarized light of intensity I0 is sent through 5 polarizers, each of the last two rotated 45 from the
previous polarizer. What is the intensity transmitted by this system?
A.
B.
C.
D.
E.
0.71 I0
0.031 I0
0.31 I0
0.125 I0
0
19. A piece of uranium can be made into nuclear explosive only after it is purified into uranium235, because
A. the other naturally occurring isotopes of uranium interfere with efficient chain reactions.
B. uranium-235 is the heaviest isotope known to mankind.
C. before purification, the uranium-235 nucleus will not split apart.
D. it has to be soldered with lead for safety.
20. The primary reason that nuclear fusion has proven difficult to adapt for commercial power
generation is that
A. the possible fuel is scarce.
B. the fuel is difficult to purify.
C. nuclei repel each other due to their positive charges.
D. the temperatures involved are too low for efficient production.
21. In a decay of 90Th232 by emission of an alpha particle, the daughter nucleus will be
A. 90Th228.
B. 92U232.
C. 88Ra228.
D. 88Ra230.
E. 87Ac232.
22. If 42 g of nitrogen reacts completely with 9 g of hydrogen (atomic weight 1) to form
ammonia (NH3), the atomic weight of nitrogen must be
A. 3.
B. 14.
C. 49.
D. 52.
E. 55.
23. A beam of white light in air passes through the transparent object shown. Dispersion is
observed to occur. From the diagram we can tell that
A. the index of refraction is larger for red light than blue.
B. the index of refraction is larger for blue light than red.
C. the object acts as a converging lens.
D. the object behaves as a concave mirror.
24. The image of an object placed 20 cm in front of a concave mirror of focal length 10 cm will
be
A. real and inverted.
B. real and erect.
C. virtual and inverted.
D. virtual and erect.
25. An object is placed 10 cm in front of a concave mirror of focal length 20 cm. The image will
be formed
A. 20 cm in front of the mirror.
B. 20 cm behind the mirror.
C. 10 cm in front of the mirror.
D. 10 cm behind the mirror.
E. 0.05 cm behind the mirror.
26. In a nuclear reactor, "chain reaction" refers primarily to
A. an out-of-control explosion.
B. the process by which the fission of one nucleus causes other nuclei to undergo fission.
C. the enrichment of uranium to make fuel for the reactor.
D. the process of heating water to create steam to generate electric power.
27. What is the source of the energy released in nuclear reactions?
A. The conversion of nuclear kinetic energy to particle potential energy.
B. Heat released during the radioactive decay process.
C. The conversion of mass to energy.
D. The binding of orbital electrons to the nuclear protons.
28. The speed of electromagnetic waves in air is 3.0  108 m/s. What is the wavelength of FM
radio waves having a frequency of 1.0  108 Hz?
A. 0.333 m
B. 1.0 m
C. 3.0 m
D. 6.0 m
E. 10 m
29. A horizontally moving positive sodium ion enters a magnetic field that points up. The
magnetic force pushes the charge out of its original path.
When viewed from the perspective of the charge, what direction will the magnetic force
point?
A. Left, into the page.
B. Right, out of the page.
C. Not enough information to answer.
30. An iPod battery is rated at 3.7 volts and operates its iPod and ear buds with a direct current of
865 milliamps. What is the power rating of this iPod?
A. 3.7 Joules per second.
B. 3.2 Watts.
C. 234 Watts.
D. 16 Watts.