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Exam 3 with Answers - How Things Work | PHYS 140, Exams of Classical Physics

University of Illinois - Urbana-ChampaignClassical Physics
Prof. Matthias Grosse Perdekamp

Material Type: Exam; Professor: Perdekamp; Class: How Things Work; Subject: Physics; University: University of Illinois - Urbana-Champaign; Term: Spring 2006;

Typology: Exams

Pre 2010

Uploaded on 03/11/2009

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Physics 140. Hour Exam III April 18, 2006
Please do not open this exam book until you are told to do so.
You will need
1. A #2 pencil
2. One scantron answer sheet
3. One exam question booklet
On the scantron answer sheet:
1. Use a #2 pencil. Do not use a mechanical pencil or pen. Darken each circle
completely, but stay within the boundary. If you decide to change an answer, erase
vigorously: The scanner sometimes registers incompletely erased marks as intended
answers, and this can adversely affect your grade. Light marks or marks extending
outside the circle may be read improperly by the scanner. Be especially careful that
your mark covers the center of its circle.
2. This Exam Booklet is Version A. Mark the A circle in the TEST FORM box near
the middle of your answer sheet. DO THIS NOW! WE WILL ASSESS A 1
POINT (RAW SCORE) PENALTY FOR FAILURE TO DO THIS.
3. Print YOUR LAST NAME in the designated spaces at the left side of the answer
sheet, and then mark the corresponding circle below each letter. Do the same for
your FIRST NAME INITIAL.
4. Print your NETWORK ID in the designated spaces at the right side of the answer
sheet, starting in the left-most column, and then mark the corresponding circle
below each character. If there is a letter "o" in your NetID, be sure to mark the "o"
circle, and not the circle for the digit zero. If and only if there is a hyphen "-" in your
NetID, mark the hyphen circle at the bottom of the column. When you have finished
marking the circles corresponding to your NetID, check particularly that you have not
marked two circles in any one of the columns.
5. Do not write in or mark the circles in any of the other boxes (STUDENT NUMBER,
DATE, SECTION, SCORES, SPECIAL CODE).
6. Mark only one answer per question.
7. When told to do so: Check to make sure that the test booklet is complete. There are
eight numbered pages, including this cover sheet.
8. If you understand the statement below, please sign (DO NOT PRINT) your name in
the space provided. If you do not understand, please ask the professor for
clarification.
Academic Integrity—Giving assistance to or receiving assistance from another
student or using unauthorized materials during a University Examination can be
grounds for disciplinary action, up to and including dismissal from the
University
Page 1 of 8 pages
(45 Problems)
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Download Exam 3 with Answers - How Things Work | PHYS 140 and more Exams Classical Physics in PDF only on Docsity!

Please do not open this exam book until you are told to do so.

You will need

1. A #2 pencil

2. One scantron answer sheet

3. One exam question booklet

On the scantron answer sheet:

1. Use a #2 pencil. Do not use a mechanical pencil or pen. Darken each circle

completely, but stay within the boundary. If you decide to change an answer, erase

vigorously: The scanner sometimes registers incompletely erased marks as intended

answers, and this can adversely affect your grade. Light marks or marks extending

outside the circle may be read improperly by the scanner. Be especially careful that

your mark covers the center of its circle.

2. This Exam Booklet is Version A. Mark the A circle in the TEST FORM box near

the middle of your answer sheet. DO THIS NOW! WE WILL ASSESS A 1

POINT (RAW SCORE) PENALTY FOR FAILURE TO DO THIS.

3. Print YOUR LAST NAME in the designated spaces at the left side of the answer

sheet, and then mark the corresponding circle below each letter. Do the same for

your FIRST NAME INITIAL.

4. Print your NETWORK ID in the designated spaces at the right side of the answer

sheet, starting in the left-most column, and then mark the corresponding circle

below each character. If there is a letter "o" in your NetID, be sure to mark the "o"

circle, and not the circle for the digit zero. If and only if there is a hyphen "-" in your

NetID, mark the hyphen circle at the bottom of the column. When you have finished

marking the circles corresponding to your NetID, check particularly that you have not

marked two circles in any one of the columns.

5. Do not write in or mark the circles in any of the other boxes (STUDENT NUMBER,

DATE, SECTION, SCORES, SPECIAL CODE).

6. Mark only one answer per question.

7. When told to do so: Check to make sure that the test booklet is complete. There are

eight numbered pages, including this cover sheet.

8. If you understand the statement below, please sign ( DO NOT PRINT ) your name in

the space provided. If you do not understand, please ask the professor for

clarification.

Academic Integrity— Giving assistance to or receiving assistance from another

student or using unauthorized materials during a University Examination can be

grounds for disciplinary action, up to and including dismissal from the

University

Page 1 of 8 pages

  1. You are a superb proposal writer and convince NASA to let you tag along to Mars with a pendulum clock in order to study gravity. Gravity on Mars is weaker than that on Earth. Compared to how it would be on Earth, the time it takes for the pendulum to compete one cycle will be A) shorter. B) longer. C) the same. D) zero.
  2. When a pendulum is oscillating with low amplitude, what does its period depend on? A) Mass and gravity. B) Length and mass. C) Length and gravity. D) Mass, length and gravity.
  3. You decide to attend an amusement park which has a ride where you are strapped into a chair which is in turn firmly attached to a plastic cable. You are released and you bounce up and down as a harmonic oscillator—a mass on the end of spring. Next in line is somebody who weighs twice as much as you do. When the heavier person goes on the ride, you notice that A) both of you will have the same period, regardless of how high you bounce. B) the heavier rider will have a longer period than the lighter one. C) the two riders will have the same period, as long as the height of their bounces is the same. D) the heavier rider will have a shorter period than the lighter one.
  4. The reason for using a harmonic oscillator as a clock's time-keeper is so that the clock will keep accurate time even if the A) frequency of the time-keeper's oscillation changes. B) stiffness of the time-keeper's restoring force changes. C) amplitude of the time-keeper's oscillation changes. D) mass of the time-keeper's moving object changes.
  5. You work in a clock shop and are dealing with an irate customer whose grandfather clock you are restoring. They notice that the period of the pendulum in their clock is 2 s and they want to double it. So they insist that you replace the pendulum with one of the same dimensions but just heavier. So you replace the mass of the pendulum with one that is twice the mass of the original. When you get the clock repaired, you and the customer check out the clock’s period and find it to be A) 2 s. B) 4 s. C) 8 s. D) 16 s.
  6. The 4 m long brass pendulum of a particular grandfather clock has a mass of 6 kilograms and completes its swing once every 3 seconds. If you were to replace the brass pendulum with a 1 m long aluminum pendulum which had a mass of 3 kilograms, it would complete its swing once every A) 1.5 seconds. B) 3 seconds. C) 6 seconds. D) 9 seconds.

Page 2 of 8 pages

  1. If you tap on a half full bottle of water you can produce a clear tone. If you pour some more water in to the bottle and try this again, the pitch (frequency) of the sound produced will A) increase. B) stay the same. C) exactly double. D) decrease.
  2. If the distance between two electric charges halves, then the force they exert on each other changes by how much? A) 4 times as large B) 2 times as large C) ½ as large D) ¼ as large
  3. One metal ball has a charge of +2 Coulombs. Another metal ball has a charge of –3 coulombs. If the balls are brought together, what is the net electric charge? A) +5 Coulombs B) –5 Coulombs C) +1 Coulombs D) – 1Coulombs
  4. After running a plastic comb through your hair several times you hold it above a small scrap of paper. The paper jumps off the table and sticks to the comb because the paper becomes A) magnetic. B) electrically charged. C) conducting. D) electrically polarized.
  5. You have just built a house out in the country and it comes to your attention that you need to install a lightning rod. Being naturally curious you ask a hardware salesperson how lightning rods work and they correctly tell you that A) they charge the house. B) they repel lightning. C) they produce corona discharges that diminish any local buildups of electrical charge. D) they use electrostatic precipitation to remove excess charge from the air.
  6. When a xerographic copier first applies electric charges to the surface of its photoconductor, it does so in the dark. The reason for applying these charges in the dark is that light exposure would A) allow the charges to flow through the photoconductor so that they wouldn’t accumulate on its surface. B) release magnetic poles that would cancel the electric charges. C) cause the magnetic poles to move, generating electricity that would neutralize the electric charges. D) cause the photoconductor to become insulating so charges will accumulate on its surface.

Page 4 of 8 pages

  1. You have covered a grounded metal surface with a layer of photoconductor. Working in the dark, you sprinkle negative charge onto this surface. If you now expose only the left half of the photoconductor to light, you will find that A) the left half becomes neutral while the right half remains negatively charged. B) nothing happens because there is no changing magnetic field. C) negative charge flows from the right side of the photoconductor to the left and both sides become neutral. D) the right half becomes neutral while the left half remains negatively charged.
  2. You measure the force between two metal balls that are fixed in space (cannot move). Metal ball A has a charge of +2 coulombs and metal ball B has a charge of -5 coulombs. You rub a glass rod with silk and then touch the glass rod to metal ball A increasing it’s charge to + 4 coulombs. The force between the balls A) Increases by a factor of 4. B) Decreases by a factor of 4. C) Increases by a factor of 2. D) Decreases by a factor of 2.
  3. In an open circuit, A) current flows normally. B) no current flows. C) electrons can take a short cut. D) only open currents can flow.
  4. You have a string of Christmas lights. One of the bulbs keeps going out but you are certain that the bulb is good. Such behavior could result from A) either an open circuit or a short. B) an open circuit only. C) a short circuit only. D) the bulb’s resistance being cut in half.
  5. A battery works because, inside of the battery, it A) creates positive charge. B) pumps positive charge from its positive terminal to its negative terminal C) creates negative charge. D) pumps positive charge from its negative terminal to its positive terminal.
  6. You remove the batteries from a working flashlight, turn both of them around as a pair, and reinsert them in the flashlight. They make good contact with the flashlight's terminals at both ends, so that there is no mechanical problem preventing the flashlight from working. If you now switch on the flashlight, it will A) not work because only electrons can actually move through a circuit. The positively charged atomic nuclei are immobile. B) work properly, although current will now be flowing backward through its circuit. C) not work because the batteries can't send current backward through the flashlight's circuit. D) not work because the light bulb can only carry electric current in one direction.

Page 5 of 8 pages

  1. A magician claims she can change a compass so that the N side points to the Geographic South Pole of the Earth. You have taken Physics 140 so you know A) this is not possible. B) this is possible and can be explained by Physics: Magic is not needed. C) this is possible and can only be explained by magic: Physics can not explain it. D) this is possible, but one needs both Physics and Magic to explain it.
  2. You have three paperclips on your desk. You push them around a bit and find that they are neither attractive nor repulsive towards each other. You now take one of the paperclips and hold it against a strong permanent magnet and then bring it close to the other two paperclips. You find the two paperclips on your desk A) are now attracted to the one you held against the magnet. B) are now repelled from the one you held against the magnet. C) are neither an attracted nor repulsed by the paperclip you held against the magnet: The paperclips behave the same as if you never held one against a permanent magnet. D) can attract or repel the paperclip you held against the magnet, depending of the orientation of the paperclips.
  3. When you drop a strong magnet through the center of a copper pipe, the magnet A) descends slowly because it is attracted to the magnetic copper metal. B) descends rapidly because its motion causes currents to flow in the pipe and those currents attract the magnet. C) falls at the usual rate because copper metal is nonmagnetic. D) descends slowly because its motion causes currents to flow in the pipe and those currents repel the magnet.
  4. If you float an aluminum pie plate (aluminum is not ferromagnetic) on the surface of a pond and move the north pole of a strong magnet in a clockwise circle just above that plate, the plate will A) begin turning counter-clockwise, as though it were being twisted away from the magnet. B) begin turning clockwise, as though it were being dragged along with the magnet. C) remain stationary. D) be lifted out of the water and will stick to the strong north pole above it.
  5. A step-up transformer has 20 primary turns and 400 secondary turns. If the primary voltage is 120 V, what is the secondary voltage? A) 48000 V B) 2400 V C) 120 V D) 6.0 V
  6. The principal advantage of sending electric power across country on very high voltage transmission lines is that A) they carry less energy per charge than low voltage transmission lines. B) electric power lost in the wires is greatly reduced. C) these transmission lines are less likely to get in the way than low voltage transmission lines— which are much closer to the ground. D) they carry much more current than low voltage transmission lines.

Page 7 of 8 pages

  1. The huge steam-powered generators found in electric power plants produce electricity by A) moving electric charges up and down inside capacitors. B) rubbing copper disks against sheets of glass. C) spinning iron cores inside of transformers. D) moving magnets past coils of wire.
  2. When a hand-crank generator is hooked up to a light bulb, the light bulb lights up when you crank the generator. You now add another light bulb to the circuit and notice that to keep both light bulbs lit A) the generator is harder to crank. B) the generator is easier to crank. C) there is no difference in the force it takes to crank the generator. D) the bulbs only light if you crank the generator in the opposite direction.
  3. In Radios, what does "AM" stand for? A) Amplification. B) Antenna Modulation. C) Antenna Modification. D) Amplitude Modulation.
  4. Why does an FM radio station do a better job of sending music to your radio than an AM radio station? A) FM is higher frequency. B) FM electronics produce better sound reproduction. C) FM has a larger bandwidth. D) FM antennas need not be as tall as AM antennas.
  5. A tank circuit A) switches energy stored between electric in the capacitor and magnetic in the resistor. B) switches energy stored between electric in the inductor and magnetic in the capacitor. C) switches energy stored between electric in the capacitor and magnetic in the inductor. D) switches energy stored between electric in the resistor and magnetic in the inductor.
  6. A radio tuner works because A) the charge sloshes back and forth in the tank circuit at a certain frequency and the station being tuned in to must be very near that frequency. B) the capacitor dimensions must be the same size as the signal wavelength. C) the magnetic field in the inductor must be the same size as that of the signal. D) the electric field in the capacitor must be the same size as that of the radio signal.
  7. A capacitor A) always acts as an insulator. B) always acts as a conductor. C) stores magnetic poles. D) stores electrical charges.
  8. You are receiving a radio signal here in Urbana from a distant radio station in New York City. The receiving antenna on your radio is connected to the signal antenna in New York by A) charges traveling between New York and Urbana. B) electromagnetic waves. C) inductors and Capacitors that are strung between the signal and receiving antennas. D) constant electric fields.

Page 8 of 8 pages

(45 Problems)

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