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Name_________________

Physics 112

Summer 2006

Exam 3

Monday, July 24

Directions:

This 60-minute exam consists of twenty multiple-choice questions. This test is worth 20% of your final grade. (One point is equal to 1% of the final grade.)

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!

41. How far are you from your image when you stand 0.75 m in front of a vertical plane mirror?

A) 0.75 m

B) 1.5 m

C) 3.0 m

D) 3.75m

E) 4.5m

42. The image formed by a plane mirror of a real object is always

A) Real, erect, and smaller then the object

B) Real, inverted, and the same size as the object

C) Real, erect, and the same size as the object

D) Virtual, inverted, and larger then the object

E) Virtual, erect and the same size as the object

43. The critical angle for a substance is measured at 53.7°. Light enters from air at 45.0°. At what angle will it continue?

A) 34.7°

B) 45.0°

C) 53.7°

D) 58.2°

E) It will not continue, but be totally reflected.

44. A concave mirror with a radius of 20 cm creates a real image 30 cm from the mirror. What is the object distance?

A) 30cm

B) 20 cm

C) 15 cm

D) 7.5 cm

E) 5.0 cm

45. When a person stands 40 cm in front of a cosmetic mirror (concave mirror), the erect image is twice the size of the object. What is the focal length of the mirror?

A) 27 cm

B) 40 cm

C) 80 cm

D) 100 cm

E) 160 cm

46. An object is placed 40 cm in front of a 20 cm focal length converging lens. How far is the image of this object from the lens?

A) 40 cm

B) 30 cm

C) 20 cm

D) 13 cm

E) 8 cm

47. Radio waves are diffracted by large objects such as buildings, whereas light is not noticeably diffracted. Why is this?

A) Radio waves are unpolarized, whereas light is plane polarized.

B) Radio waves are polarized, whereas light is plane unpolarized.

C) Radio waves are coherent and light is usually not coherent.

D) The wavelength of light is much greater than the wavelength of radio waves.

E) The wavelength of light is much smaller than the wavelength of radio waves.

48. A beam of light (f = 5.0 × 1014 Hz) enters a piece of glass (n = 1.5). What is the frequency of the light while it is in the glass?

A) 5.0 × 1014 Hz

B) 7.5 × 1014 Hz

C) 3.3 × 1014 Hz

D) 1.0 × 1014 Hz

E) 2.5 × 1014 Hz

49. 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) 7.5 cm

50. In a single slit diffraction experiment, if the width of the slit increases, what happens to the width of the central maximum on a screen?

A) It increases.

B) It decreases.

C) It remains the same.

D) It depends from the distance to the screen.

E) There is not enough information to determine.

51. In order to obtain a good single slit diffraction pattern, the slit width could be:

A) (/100

B) (/10

C) (

D) 10(

E) 100(

52. Two stars 15 light-years away are barely resolved by a 55-cm (mirror diameter) telescope. How far apart are the stars? Assume [pic] and that the resolution is limited by diffraction. (1 light-year = 9.46x1015 m)

A) 1.3x107 m

B) 1.4x108 m

C) 1.5x109 m

D) 1.6x1010 m

E) 1.7x1011 m

53. A diffraction grating has 5000 lines per cm. The angle between the central maximum and the fourth order maximum is 47.2°. What is the wavelength of the light?

A) 138 nm

B) 183 nm

C) 367 nm

D) 637 nm

E) 711 nm

54. What is the minimum thickness of a nonreflecting film coating (n = 1.30) on a glass lens (n = 1.50) for wavelength 500 nm?

A) 250 nm

B) 192 nm

C) 167 nm

D) 96.2 nm

E) 57.3 nm

55. An ideal polarizer is placed in a beam of unpolarized light and the intensity of the transmitted light is 1. A second ideal polarizer is placed in the beam with its referred direction rotated 40° to that of the first polarizer. What is the intensity of the beam after it has passed through both polarizers?

A) 0.77

B) 0.64

C) 0.59

D) 0.41

E) 0.36

56. A beam of unpolarized light in air strikes a flat piece of glass at an angle of 57.3°. If the reflected beam is completely polarized, what is the index of refraction of the glass?

A) 1.50

B) 1.52

C) 1.54

D) 1.56

E) 1.58

57. A near-sighted person has a far point of 20 cm. What lens (in diopters) will allow this person to see distant objects clearly? Assume that the lens is 2.0 cm from the eye (typical for eyeglasses)

A) + 5.6 D

B) - 5.6 D

C) + 0.056 D

D) - 0.056 D

E) -5.0 D

58. A magnifying glass with a focal length of 8.5 cm is used to read print placed at a distance 7.5 cm. Calculate the angular magnification.

A) 2.3x

B) 3.3x

C) 4.3x

D) 5.3x

E) 6.3x

59. Estimate the peak wavelength for radiation from a floodlamp at 3500 K.

A) 450 nm

B) 521 nm

C) 736 nm

D) 829 nm

E) 901 nm

60. The work function for a certain sample is 2.3 eV. What is the stopping potential for electrons ejected from the sample by 7.0x1014 Hz electromagnetic radiation?

A) 9.0 V

B) 6.0 V

C) 3.0 V

D) 1.0 V

E) 0.6 V

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

|41 |51 |

|42 |52 |

|43 |53 |

|44 |54 |

|45 |55 |

|46 |56 |

|47 |57 |

|48 |58 |

|49 |59 |

|50 |60 |

Answer Sheet

|41 |51 |

|B) 1.5 m |D) 10( |

|42 |52 |

|E) Virtual, erect and the same size as |E) 1.7x1011 m |

|the object | |

|43 |53 |

|A) 34.7° |C) 367 nm |

|44 |54 |

|C) 15 cm |D) 96.2 nm |

|45 |55 |

|C) 80 cm |C) 0.59 |

|46 |56 |

|A) 40 cm |D) 1.56 |

|47 |57 |

|E) The wavelength of light is much |B) - 5.6 D |

|smaller than the wavelength of radio | |

|waves. | |

|48 |58 |

|A) 5.0 × 1014 Hz |B) 3.3x |

|49 |59 |

|B) 3.0 cm |D) 829 nm |

|50 |60 |

|B) It decreases. |E) 0.6 V |

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