Physics 112 / Exam 4 / Summer 2009

Physics 112

Summer 2009

Exam 4

Thursday, August 6

Directions:

This exam consists of thirty multiple-choice questions.

The questions on this test are not in order of difficulty.

You must mark all of your answers on both your test and answer sheet.

In marking the multiple choice bubble sheet use a number 2 pencil. Do not use ink. If you did not bring a pencil, ask for one. Fill in the appropriate circles completely. If you need to change any entry, you must completely erase your previous entry.

Carefully read each question and its five possible answers. Select one and only one answer for each question. Choose the answer that is closest to the correct one.

You have a sheet in the back of the test that you may use for any extra rough work.

When you are finished with the exam, place all exam materials, including the bubble sheet, the exam itself, and scratch paper that you used for the exam, in your folder and return the folder.

Good luck!

  1. Three identical charges of 3.0 μC are placed at the vertices of an equilateral triangle which measures 30 cm on a side. What is the magnitude of the electrostatic force which acts on any one of the charges?

A) 1.6 N

B) 1.8 N

C) 2.0 N

D) 2.2 N

E) 2.4 N

  1. A solid block of metal in electrostatic equilibrium is placed in a uniform electric field. Give a statement concerning the electric field in the block's interior.

A) The interior field points in a direction opposite to the exterior field and is bigger.

B) The interior field points in a direction opposite to the exterior field and is smaller.

C) The interior points in a direction that is parallel to the exterior field and is bigger.

D) The interior points in a direction that is parallel to the exterior field and is smaller.

E) There is no electric field in the block's interior.

  1. A uniform electric field, with a magnitude of 500 V/m, is directed parallel to the +x axis. If the potential at x = 5.0 m is 2500 V, what is the potential at x = 2.0 m?

A) 500 V

B) 1000 V

C) 2000 V

D) 4000 V

E) 5000 V

  1. A battery charges a parallel-plate capacitor fully and then is removed. The plates are immediately pulled apart. (With the battery disconnected, the amount of charge on the plates remains constant.) What happens to the potential difference between the plates as they are being separated?

A) It increases.

B) It decreases.

C) It remains constant.

D) It is zero.

E) Cannot be determined from the information given

  1. Consider two copper wires. One has twice the length and twice the cross-sectional area of the other. How do the resistances of these two wires compare?

A) Both wires have the same resistance

B) The longer wire has twice the resistance of the shorter wire

C) The longer wire has four times the resistance of the shorter wire

D) Theshorter wire has twice the resistance of the longer wire

E) Theshorter wire has four times the resistance of the longer wire

  1. Two resistors of 15 and 30 Ω are connected in parallel. If the combination is connected in series with a 9.0-V battery and a 20-Ω resistor, what is the current through the 15-Ω resistor?

A) 0.10 A

B) 0.13 A

C) 0.20 A

D) 0.26 A

E) 0.30 A

  1. A 4.0-MΩ resistor is connected in series with a 0.50-μF capacitor. The capacitor is initially uncharged. The RC combination is charged by a 9.0-V battery. What is the change in voltage between t = RC and t = 3RC?

A) 11 V

B) 7.6 V

C) 5.7 V

D) 2.9 V

E) 1.3 V

  1. The force on a current-carrying wire in a magnetic field is the strongest when

A) the current is parallel to the field lines

B) the current is at a 30° angle with respect to the field lines

C) the current is at a 45° angle with respect to the field lines

C) the current is at a 60° angle with respect to the field lines

E) the current is perpendicular to the field lines

  1. Two long parallel wires carry currents of 20 A and 5.0 A in opposite directions. The wires are separated by 0.20 m. At what point between the two wires are the contributions to the magnetic field equal?

A) 0.040 m from the 20 A wire

B) 0.080 m from the 20 A wire

C) 0.12 m from the 20 A wire

D) 0.16 m from the 20 A wire

E) 0.18 m from the 20 A wire

  1. An airplane with a wing span of 60 m flies horizontally at a location where the downward component of the Earth's magnetic field is 6.0 × 10-5 T. Find the magnitude of the induced emf between the tips of the wings when the speed of the plane is 225 m/s.

A) 0.41 V

B) 0.61 V

C) 0.81 V

D) 1.2 V

E) 1.4 V

  1. A bar magnet falls through a loop of wire with the north pole entering first. As the north pole enters the wire, the induced current will be (as viewed from above)

A) zero

B) clockwise

C) counterclockwise

D) to top of loop

E) a current whose direction cannot be determined from the information given

  1. What is the current through a 2.50-mH coil due to a 110-V, 60.0 Hz source?

A) 0.94 A

B) 2.5 A

C) 104 A

D) 117 A

E) 153 A

  1. What is the frequency of 20 mm microwaves?

A) 100 MHz

B) 400 MHz

C) 15 GHz

D) 73 GHz

E) 98 GHz

  1. Is it possible to see a virtual image?

A)No, since the rays that seem to emanate from a virtual image do not in fact emanate from the image.

B)No, since virtual images do not really exist.

C)Yes, the rays that appear to emanate from a virtual image can be focused on the retina just like those from an illuminated object.

D)Yes, since almost everything we see is virtual because most things do not themselves give off light, but only reflect light coming from some other source.

E)Yes, but only indirectly in the sense that if the virtual image is formed on a sheet of photographic film, one could later look at the picture formed.

  1. A converging lens has a focal length f. An object is placed between f and 2f on the axis. The image formed is located

A) at 2f

B) between f and 2f

C) at f

D) at a distance greater than 2f from the lens

E) at a distance smaller than f from the lens

  1. In a Young's double slit experiment, if the separation between the two slits is 0.050 mm and the distance from the slits to a screen is 2.5 m, find the spacing between the first-order and second-order bright fringes for light with wavelength of 600 nm.

A) 1.5 cm

B) 3.0 cm

C) 4.5 cm

D) 6.0 cm

E) 7.0 cm

  1. A soap bubble has an index of refraction of 1.33. What minimum thickness of this bubble will ensure maximum reflectance of normally incident 530 nm wavelength light?

A) 24.9 nm

B) 99.6 nm

C) 199 nm

D) 398 nm

E) 420 nm

  1. Unpolarized light is passed through a polarizer-analyzer combination. The transmission axes of the polarizer and the analyzer are at 30.0° to each other. What percentage of the unpolarized light gets through the combination?

A) 37.5%

B) 50%

C) 75%

D) 84.5%

E) 100%

  1. An important reason for using a very large diameter objective in an astronomical telescope is

A) to increase the magnification.

B) to increase the resolution.

C) to form a virtual image, which is easier to look at.

D) to increase the width of the field of view.

E) to increase the depth of the field of view.

  1. A farsighted person can read a newspaper held 25 cm from his eyes, if he wears glasses of +3.33 diopters. What is this person's near point?

A) 4.2 cm

B) 25 cm

C) 31 cm

D) 1.0 m

E) 1.5 m

  1. When light of wavelength 350 nm is incident on a metal surface, the stopping potential of the photoelectrons is 0.500 V. What is the threshold frequency?

A) 3.47 × 1014 Hz

B) 3.74 × 1014 Hz

C) 4.73 × 1014 Hz

D) 7.36 × 1014 Hz

E) 9.21× 1014 Hz

  1. What is the energy difference between the second excited state and first excited state of an electron in the “box” of size L=1nm?

A) 1.9 eV

B) 1.1 eV

C) 0.6 eV

D) 0.3 eV

E) 0.2 eV

  1. In making a transition from state n = 1 to state n = 2, the hydrogen atom must

A) absorb a photon of energy 10.2 eV.

B) emit a photon of energy 10.2 eV.

C) absorb a photon of energy 13.6 eV.

D) emit a photon of energy 13.6 eV.

E) absorb a photon of energy 27.2 eV.

  1. An electron has a wavelength of 0.123 nm. What is its energy in eV? (This energy is not in the relativistic region.)

A) 20 eV

B) 60 eV

C) 80 eV

D) 100 eV

E) 120 eV

  1. The probability of finding an electron in a hydrogen atom is directly proportional to its

A) energy

B) momentum

C) angular momentum

D) wave function

E)square of the wave function

  1. A neutral atom has an electron configuration of 1s22s22p6. If a neutral atom holds one additional electron, what is the ground state configuration?

A) 1s22s22p63s1

B) 1s22s22p7

C) 1s22s32p6

D) 1s32s22p6

E)none of the given answers

  1. The binding energy per nucleon

A) increases steadily as we go to heavier elements.

B) decreases steadily as we go to heavier elements.

C) is approximately constant throughout the periodic table, except for very light nuclei.

D) has a maximum near iron in the periodic table.

E) is a periodic function

  1. Compared to the masses of its separate protons and neutrons, the total mass of a stable nucleus is always

A) less

B) the same

C) greater

D) zero

E) could be less or grater

  1. If the half-life of a material is 45 years, how much will be left after 100 years?

A) more than 1/2

B) less than 1/2but more then 1/3

C) less than 1/3 butmore than 1/4

D) less than 1/4

E)zero

  1. What is the Q-value of the following reaction?

14N+4He=1p+17O

(14.003074)(4.002603)(1.007825)(16.999131)

A) 1.191 MeV

B) -1.191 MeV

C) 1.279 × 10-3 MeV

D) -1.279 × 10-3 MeV

E)zero

Scratch Paper (intentionally left blank)

Record Sheet

You may fill in this sheet with your choices, detach it and take it with you after the exam for comparison with the posted answers

61 / 71 / 81
62 / 72 / 82
63 / 73 / 83
64 / 74 / 84
65 / 75 / 85
66 / 76 / 86
67 / 77 / 87
68 / 78 / 88
69 / 79 / 89
70 / 80 / 90

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