### Summer 2001 Physics 102 Hour Exam 3(22 questions)

The grading button and a description of the scoring criteria are at the bottom of this page. Basic questions are marked by a single star *. More difficult questions are marked by two stars **. The most challenging questions are marked by three stars ***.

This exam consists of 22 questions; true-false questions are worth 2 points each, three-choice multiple choice questions are worth 3 points each, five-choice multiple choice questions are worth 6 points each. The maximum possible score is 120. When the exam was given, the mean was 72.9; the median was 78. Click here to see page1 page2 of the formula sheet that came with the exam.

### QUESTION 1**

In a stack of three polarizing sheets the first and third are crossed while the middle one has its axis at 45° to the axes of the other two. The fraction of the intensity of an incident unpolarized beam of light that is transmitted by the stack is:

(a)   1/2
(b)   1/3
(c)   1/4
(d)   1/8
(e)   zero

### QUESTION 2*

Radio waves of wavelength 300 m have a frequency of:

(a)   10-6 kHz
(b)   500 kHz
(c)   1000 kHz
(d)   9000 kHz
(e)   108 kHz

### QUESTION 3**

Polaroid sunglasses are most effective when the transmission axis of the polaroid is:

(a)   vertical
(b)   horizontal
(c)   at 30° with the vertical
(d)   at 45° with the vertical
(e)   at 60° with the vertical

### QUESTION 4*

The diagram shows the passage of a ray of light from air into a substance X. Take the refractive index of air to be 1.0. The index of refraction of material X is

(a)   0.74
(b)   1.15
(c)   1.29
(d)   1.35
(e)   1.47

### QUESTION 5*

Which diagram illustrates the path of a light ray as it travels from a given point X in air to another given point Y in glass?

(a)
(b)
(c)
(d)
(e)

### QUESTION 6**

The rectangular metal tank shown is filled with an unknown liquid. The observer, whose eye is level with the top of the tank, can just see corner E. Take the index of refraction of air to be 1.0. The index of refraction of this liquid is

(a)   1.75
(b)   1.67
(c)   1.50
(d)   1.33
(e)   1.25

### QUESTION 7***

The two lenses shown are illuminated by a beam of parallel light from the left.

The beam emerging from lens B is

(a)   parallel.
(b)   diverging.
(c)   converging.

### QUESTION 8*

A nearsighted person can see clearly only objects within 6 feet of her eye. To see distant objects, she should wear eyeglasses of what type and focal length?

(a)   diverging, 12 ft
(b)   diverging, 6 ft
(c)   converging, 12 ft
(d)   converging, 6 ft
(e)   diverging, 3 ft

### QUESTION 9***

When a simple camera is focussed on a distant object, the lens to film distance is found to be 40.0 mm. To focus on an object 0.54 m in front of the lens, the film to lens distance must be

(a)   not changed.
(b)   decreased by 2.7 mm.
(c)   decreased by 3.2 mm.
(d)   increased by 2.7 mm.
(e)   increased by 3.2 mm.

### QUESTION 10***

A soap film, 4 × 10-5 cm thick, is illuminated by white light normal to its surface. The index of refraction of the film is 1.50. Which wavelengths will be intensified in the reflected beam?

(a)   4000 A and 6000 A
(b)   4800 A and 8000 A
(c)   3600 A and 5333 A
(d)   4000 A and 8000 A
(e)   5100 A and 7200 A

### QUESTION 11**

The object-lens distance, for a converging lens, is 400 mm. The image is three times the size of the object. To make the image five times the size of the object, the object-lens distance must be changed to

(a)   360 mm
(b)   540 mm
(c)   600 mm
(d)   720 mm
(e)   960 mm

### QUESTION 12**

For an eye that cannot focus on objects more than 25 cm in front of it, the power in diopters of the lens needed for distinct distant vision is

(a)   +25
(b)   +4.0
(c)   -4.0
(d)   -2.5
(e)   none of these

### QUESTION 13*

Consider the photoelectric effect in silver. The minimum frequency that light must have to eject electrons from the surface is 1.14 × 1015 Hz. Find the work function of silver.

(a)   9.46 eV
(b)   2.37 eV
(c)   5.23 eV
(d)   1.76 eV
(e)   4.73 eV

### QUESTION 14*

A ray is being refracted from a medium 1 of unknown index of refraction n1 into a medium 2 with an index of refraction n2 = 1.026. The speed of light in medium 1 is:

(a)   3 × 108 m/s
(b)   1.596 × 108 m/s
(c)   1.065 × 108 m/s
(d)   8.457 × 108 m/s
(e)   2 × 108 m/s

### QUESTION 15**

When a person holds a concave mirror 20 cm from his/her face, an image of his/her face is produced which is inverted and enlarged by a factor of two. Determine the focal length (in cm) of the spherical mirror.

(a)   +10.0
(b)   +13.3
(c)   +20.0
(d)   +40.0
(e)   -40.0

### QUESTION 16***

Plane polarized light in air is incident at the Brewster angle on a plate of glass (n = 1.5). The reflected light has zero intensity if the direction of polarization is oriented to the plane of incidence at:

(a)   0°
(b)   56.3°
(c)   90°
(d)   any angle
(e)   no angle

### QUESTION 17*

White light passes through the prism as shown below. The color which suffers minimum deviation is:

(a)   red
(b)   yellow
(c)   green
(d)   blue
(e)   violet

### QUESTION 18**

This and the next question are about the same situation:

Red light emitted by hydrogen atoms at rest in the laboratory has wavelength 656 nm. Light emitted in the same process on a distant galaxy is received at Earth with wavelength 708 nm. The galaxy is moving

(a)   towards Earth.
(b)   away from Earth.
(c)   not moving relative to Earth.

### QUESTION 19**

What is the speed of the galaxy relative to Earth in terms of the speed of light in vacuum c?

(a)   0c
(b)   0.074c
(c)   0.148c
(d)   1.58c
(e)   0.04c

### QUESTION 20***

This and the next two questions are about the same situation:

Blue light with wavelength l = 380 × 10-9 m is incident upon two narrow slits separated by a distance d before striking a screen 5.2 meters away. The spacing between the slits is d = 1.10 × 10-3 m. Calculate the distance y between the central bright fringe and first dark. (You may approximate sin(q) » tan(q) » q).

(a)   y = 0.9 × 10-3 m
(b)   y = 1.8 × 10-3 m
(c)   y = 2.6 × 10-3 m
(d)   y = 3.6 × 10-3 m
(e)   y = 7.2 × 10-3 m

### QUESTION 21*

Now red light (l = 650 × 10-9 m) is incident on the same two slits, the distance y between the central bright fringe and the first dark fringe

(a)   decreases.
(b)   remains the same.
(c)   increases

### QUESTION 22***

Now the two slits are replaced by a single slit with width w = d, and illuminated with the original blue light. The distance y to the first dark fringe

(a)   decreases.
(b)   remains the same.
(c)   increases.

Scoring of True-False (T,F) Questions:
• If you mark the correct answer, you get 2 points.
• If you mark the wrong answer or if you mark neither answer, you get 0 points.
Scoring of Multiple Choice I (a,b,c) Questions:
• If you mark the correct answer, you get 3 points.
• If you mark a wrong answer or if you mark none of the answers, you get 0 points.
Scoring of Multiple Choice II (a,b,c,d,e) Questions:
• If you mark one answer and it is the correct answer, you get 6 points.
• If you mark two answers and one of them is the correct answer, you get 3 points.
• If you mark three answers and one of them is the correct answer, you get 2 points.
• If you do not mark the correct answer, or if you mark more than three answers, or if you mark none of the answers, you get 0 points.