Fall 2004 Physics 102 Hour Exam 3
(27 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 ***.

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 108. The exam period was 90 minutes; the mean was 89.0; the median was 92. Click here to see page1 page2 of the formula sheet that came with the exam.


QUESTION 1*

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

As shown below, a slide projector is used to produce an image of an object on a screen.

If the image is focused by moving only the object, what should be the distance between the object and the lens so that the image is focused at the screen?

(a)   1.823 cm
(b)   4.018 cm
(c)   5.292 cm
(d)   6.321 cm
(e)   7.827 cm


QUESTION 2*

How large will the image appear on the screen when it is in focus?

(a)   0.89 m
(b)   1.02 m
(c)   2.24 m
(d)   5.34 m
(e)   9.99 m


QUESTION 3*

Will the image of the tip of the arrow appear towards the top or the bottom of this page?

(a)   top
(b)   bottom


QUESTION 4*

This and the next question concern the following situation:

In the picture above, a ray of light is coupled into an optical fiber consisting of two types of glass. The light is aimed at the fiber so that the ray makes an angle θ with the normal to the face of the fiber. What is the maximum value of θ for which the light is totally internally reflected at location a?

(a)   10.01°
(b)   32.58°
(c)   45.21°
(d)   62.98°
(e)   77.55°


QUESTION 5*

If the index of refraction of the outer layer of glass (the "cladding") were decreased, would the maximum value for θ for which the light would totally internally reflect at a decrease, increase, or stay the same?

(a)   decrease
(b)   stay the same
(c)   increase


QUESTION 6**

Which one of these three ray tracing diagrams is most accurate?

(a)   
(b)   
(c)   


QUESTION 7*

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

An object is placed 20 cm in front of a convex mirror whose radius of curvature is 10 cm.

The image is located

(a)   5 cm to the left of the mirror.
(b)   2 cm to the left of the mirror.
(c)   on the mirror.
(d)   4 cm to the right of the mirror.
(e)   6 cm to the right of the mirror.


QUESTION 8*

The image is

(a)   upright.
(b)   inverted.


QUESTION 9**

If the object and mirror were immersed in water rather than air, the image would be located

(a)   closer to the mirror.
(b)   further from the mirror.
(c)   at the same distance from the mirror.


QUESTION 10**

A red and a blue pulse of light are launched from two lasers that are the same distance away from a gold mirror that is deposited onto a piece of glass. The direction of propagation of the pulses of light is normal to the face of the glass. Which one of the following statements is true?

(a)   The red pulse will return to its initial location first.
(b)   The blue pulse will return to its initial location first.
(c)   Both pulses will return to their initial locations at the same time.


QUESTION 11*

A near-sighted person has a far point of 5 m. What is the focal length of the contact lenses that will correct her vision?

(a)   -7 m
(b)   -5 m
(c)   -1 m
(d)   6 m
(e)   10 m


QUESTION 12*

This and the next question are about the following situation:

An object of 6 cm height is at a position 12 cm away from a spherical concave mirror. The focal length of the mirror is 8 cm. The locations of the center of curvature (C) and the focal point (F) are indicated.

What is the height of the image?

(a)   6 cm
(b)   8 cm
(c)   12 cm
(d)   16 cm
(e)   20 cm


QUESTION 13*

The image is

(a)   real.
(b)   virtual.


QUESTION 14*

Light of wavelength λ = 500 nm is incident on a single slit of width w = 700 μm and produces a diffraction pattern on a screen 3.5 m away. What is the distance, d, between the central bright fringe and the first dark fringe?

(a)   d = 0.35 mm
(b)   d = 1.19 mm
(c)   d = 1.77 mm
(d)   d = 2.50 mm
(e)   d = 2.99 mm


QUESTION 15**

A far-sighted person wears contact lenses to correct her vision. Her lens prescription is old, and her near point has increased. Should the optometrist prescribe new lenses with a larger or smaller diopter compared with the lenses that she has now?

(a)   larger
(b)   smaller


QUESTION 16**

This and the next question concern the following situation:

The person in the figure below is 2 m tall. A mirror is located 20 m away and is 0.5 m tall. The top of the mirror is at the same height as the top of the personís head. Assume for simplicity that the personís eyes are at the height of the top of her head.

What part of her body does the person see in the mirror?

(a)   top 0.25 m
(b)   top 0.5 m
(c)   top 1 m
(d)   top 1.5 m
(e)   entire 2 m


QUESTION 17*

If the person backs up from the mirror, she can see

(a)   more of herself in the mirror.
(b)   less of herself in the mirror.
(c)   the same amount of herself in the mirror.


QUESTION 18*

This and the next question concern the following situation:

A ray of light passes through a series of media with different refractive indices, n1, n2 and n3. It then enters a medium with an index of refraction n1 as shown.

In which medium does the light travel the slowest?

(a)   medium with index n1
(b)   medium with index n2
(c)   medium with index n3


QUESTION 19*

What is the relationship between the angles θA and θB?

(a)   θA > θB
(b)   θA < θB
(c)   θA = θB


QUESTION 20**

This and the next two questions concern the following situation:

If you go to the Art Institute of Chicago, you can admire paintings by the French painter Georges Seurat. For his work, Seurat uses small dots of color to produce an image. At a distance of a few meters, the eye cannot resolve these dots. You thus see a "smooth" picture.

If each dot is the same size, which color dots are the easiest to resolve?

(a)   Red (λ= 660 nm)
(b)   Green (λ = 550 nm)
(c)   Blue (λ = 470 nm)


QUESTION 21**

The diameter of the green (λ = 550 nm) dots in the painting is d = 2.0 mm and the dots are touching each other, as shown in the figure below. What is the maximum distance, L, a person with normal, unaided vision (near point 25 cm, far point infinity, pupil diameter 2.0 mm) can stand from the painting to resolve the individual green dots?

(a)   L = 1.44 m
(b)   L = 2.31 m
(c)   L = 3.27 m
(d)   L = 4.89 m
(e)   L = 5.96 m


QUESTION 22*

Let L be the answer to the previous question. If the diameter of the green dots were 1.0 mm instead of 2.0 mm, the maximum distance a person with normal, unaided vision (near point 25 cm, far point infinity, pupil diameter 2.0 mm) can stand from the painting to resolve the individual green dots would be

(a)   smaller than L.
(b)   equal to L.
(c)   larger than L.


QUESTION 23*

This and the next two questions concern the following situation:

A flat thin plate of thickness d and index of refraction n1 = 1.6 is placed on a flat thick plate with index of refraction n2 = 1.2, as shown in the figure below. When monochromatic light of wavelength 720 nm in air is normally incident on the plates, no light is reflected from the plates. Ignore the reflection at the bottom of the thick plate. The whole system is in air (index of refraction n = 1.0).

What is the minimum thickness of the thin plate?

(a)   d = 131 nm
(b)   d = 225 nm
(c)   d = 333 nm
(d)   d = 417 nm
(e)   d = 498 nm


QUESTION 24**

Let d be the answer to the previous question. If the top plate were replaced by a similar plate with thickness d and index of refraction n1 = 1.4, and if the bottom thick plate were kept the same, some light of wavelength 720 nm would be reflected.

(T)   True
(F)   False


QUESTION 25**

If the original system with indexes of refraction n1 = 1.6 and n2 = 1.2 were placed in water (index of refraction n = 1.33), some light of wavelength 720 nm in air would be reflected.

(T)   True
(F)   False


QUESTION 26*

This and the next question concern the following situation:

Red light with wavelength λ = 680 nm is incident upon two narrow slits separated by a distance d = 0.40 mm before striking a screen. The distance between the central bright fringe and first dark fringe is 5.0 mm. The whole apparatus is in air (index of refraction n = 1.0).

Calculate L, the distance between the slits and the screen. (You may approximate sin(θ) ≈ tan(θ) ≈ θ.)

(a)   L = 5.88 m
(b)   L = 6.12 m
(c)   L = 7.45 m
(d)   L = 8.99 m
(e)   L = 9.13 m


QUESTION 27**

If the whole apparatus were placed in water (index of refraction n = 1.33), the distance between the central bright fringe and first dark fringe would be

(a)   less than 5.0 mm.
(b)   equal to 5.0 mm.
(c)   greater than 5.0 mm.