### Fall 2000 Physics 102 Hour Exam 3(29 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 29 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 116. When the exam was given, the mean was 92.6; the median was 93. Click here to see page1 page2 of the formula sheet that came with the exam.

### QUESTION 1**

When you stand in front of a convex mirror, your image is always reduced.

(T)   True
(F)   False

### QUESTION 2*

When you stand in front of a concave mirror, your image is always enlarged.

(T)   True
(F)   False

### QUESTION 3**

The speed of light in glass depends on the color of the light.

(T)   True
(F)   False

### QUESTION 4*

The index of refraction for diamond is 2.5, and the index of refraction for water is 1.33. Is it possible for light to undergo total internal reflection traveling from the water to the diamond?

(a)   Yes
(b)   No

### QUESTION 5*

This and the next question pertain to the following physical situation:

Reading glasses with a power of +2.3 diopters are used to help a far-sighted person see text at a comfortable distance of 30 cm in front of her eyes. Without the glasses, the closest she can see clearly is

(a)   37 cm
(b)   67 cm
(c)   97 cm

### QUESTION 6*

These glasses would look most closely like which figure?

(a)
(b)

### QUESTION 7*

Two rays start in material #1 and pass through material #2 into material #3. The correct relation between the indices of refraction of the three materials is:

(a)   n1 < n2 < n3
(b)   n1 > n2 > n3
(c)   n1 < n2 > n3

### QUESTION 8*

Which of the rays shown reflecting off the mirror in this diagram is incorrect?

(a)   #1
(b)   #2
(c)   #3
(d)   #4
(e)   #5

### QUESTION 9*

This and the next two questions pertain to the following situation:

An inverted image is 2/3 as large as the original object, which is positioned 23 cm in front of a concave spherical mirror. What is the focal length of this mirror?

(a)   4.4 cm
(b)   9.2 cm
(c)   11.1 cm
(d)   17.6 cm
(e)   32.1 cm

### QUESTION 10*

Suppose the mirror above and the object in front of it were both placed under water. The image would

(a)   move closer to the mirror.
(b)   move further from the mirror.
(c)   remain the at same location.

### QUESTION 11*

Light of wavelength l = 444 nm incident on a double slit with separation 0.15 mm creates a series of bright fringes separated by 5 mm on a screen. The distance from the slits to the screen is:

(a)   0.57 m
(b)   1.17 m
(c)   1.33 m
(d)   1.69 m
(e)   2.45 m

### QUESTION 12*

Light with the same wavelength l = 444 nm in air constructively-interferes from a thin plastic coating (n = 1.2) on a thick glass plate (n = 1.4). Find the minimum (non-zero) thickness of the coating.

(a)   111 nm
(b)   185 nm
(c)   222 nm
(d)   370 nm
(e)   444 nm

### QUESTION 13*

This and the next two questions pertain to the following situation:

The figure below shows a diverging lens with a focal length of -2 cm. The object is located 5 cm to the left of the lens.

The image formed by the lens will be

(a)   real.
(b)   virtual.

### QUESTION 14**

The image formed by the lens will be

(a)   upright.
(b)   inverted.

### QUESTION 15*

If the original object is 2.2 cm tall, how big is the image?

(a)   0.63 cm
(b)   1.44 cm
(c)   3.10 cm

### QUESTION 16*

A binary star in the constellation Orion has an angular separation of 1 × 10-5 radians. At a wavelength of 500 nm, the smallest circular aperture that will resolve the two stars has diameter:

(a)   1.8 cm
(b)   3.0 cm
(c)   4.2 cm
(d)   5.0 cm
(e)   6.1 cm

### QUESTION 17*

This and the next two questions pertain to the following situation:

There are two layers of transparent materials surrounded by air. The bottom layer is glass with refractive index n1 = 1.5. The top layer is a plastic with refractive index n2 = 2.07. A beam of light enters from the bottom layer with an incidence angle of 45°.

What is the angle q of the beam inside the plastic?

(a)   14°
(b)   20°
(c)   26°

### QUESTION 18*

In the diagram, several possible rays for the light beam exiting the plastic are indicated. Why ray best represents the actual exit path of the beam?

(a)
(b)
(c)

### QUESTION 19*

What is the critical angle between the plastic and the air above?

(a)   28.8°
(b)   46.3°
(c)   66.1°

### QUESTION 20*

This and the next three questions pertain to the following situation:

An object of height 0.05 meters is located 0.6 meters in front of a thin converging lens. The lens forms an image of the object at point A, which is 0.3 meters beyond the lens.

What is the focal length of the lens?

(a)   0.40 m
(b)   0.20 m
(c)   0.15 m

### QUESTION 21*

What is the height of the image formed at position A?

(a)   0.025 m
(b)   0.050 m
(c)   0.075 m

### QUESTION 22*

When the object is moved slightly closer to the lens, the image will

(a)   increase in size and move closer to the lens.
(b)   increase in size and move farther away from the lens.
(c)   decrease in size and move closer to the lens.
(d)   decrease in size and move farther away from the lens.
(e)   stay in the same place.

### QUESTION 23*

If we add a second converging lens with a focal length of 0.6 meters at point B, where will the final image form?

(a)   0.6 m left of the second lens
(b)   0.2 m left of the second lens
(c)   0.2 m right of the second lens
(d)   0.6 m right of the second lens
(e)   0.9 m right of the second lens

### QUESTION 24**

The rearview mirror on a car is 10 cm high and is located 50 cm in front of the driver. To see the full image of a truck of height 3 m, the distance between the mirror and the truck must be:

(a)   6.0 m
(b)   9.9 m
(c)   12.6 m
(d)   14.5 m
(e)   17.4 m

### QUESTION 25*

An object is located in front of a convex mirror as shown, with the center of curvature C and focal point F indicated.

The image is formed at location:

(a)   #1
(b)   #2
(c)   #3
(d)   #4
(e)   #5

### QUESTION 26***

Light of wavelength 625 nm is incident on a two parallel slits spaced by 4 mm. The intensity on a screen behind the grating is shown. The width of each slit is:

(a)   200 µm
(b)   333 µm
(c)   400 µm
(d)   500 µm
(e)   800 µm

### QUESTION 27**

Light with a wavelength in air of 500 nm is incident normal to a glass slab of thickness 100 µm as shown. The index of refraction of the glass is 1.44. The number of wavelengths of light inside the glass plate is:

(a)   100
(b)   139
(c)   200
(d)   288
(e)   400

### QUESTION 28**

This and the next question pertain to the following situation:

An air wedge is formed by two thick optical plates in contact at one end and separated at the other as shown. The plates have index of refraction 1.5. When monochromatic light of wavelength 500 nm in air is incident on the plates, a series of dark parallel lines is observed.

What is the separation of the plates at the location of the 72nd dark line to the right of the contact edge?

(a)   18 µm
(b)   24 µm
(c)   36 µm
(d)   54 µm
(e)   108 µm

### QUESTION 29**

The wedge is filled with water of index of refraction 1.33. The total number of dark lines

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

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.