### Fall 2002 Physics 102 Hour Exam 3(32 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 32 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 97. The exam period was 90 minutes; the mean was 78.5; the median was 81. Click here to see page1 page2 of the formula sheet that came with the exam.

### QUESTION 1**

Blue light travels through glass ___________ red light.

(a)   faster than
(b)   at the same speed as
(c)   slower than

### QUESTION 2*

The image of an object in a convex mirror is

(a)   always enlarged.
(b)   always reduced.
(c)   sometimes reduced, sometimes enlarged, depending upon the distance from the object to the mirror.

### QUESTION 3*

Light passes down through three layers of transparent materials, as shown below, each with a different index of refraction. At which interface is total internal reflection possible?

(a)   A (from n=1.3 to n=1.4)
(b)   B (from n=1.4 to n=1.2)

### QUESTION 4**

This and the next question are about the following situation:

A film of oil of thickness t is floating on water. The index of refraction is 1.0, 1.45, and 1.33 for air, oil, and water, respectively. A person views the film from the air in a direction normal to the surface.

The person sees that there is constructive interference of reflected light of wavelength 630 nm. What is the minimum thickness t of the oil film?

(a)   109 nm
(b)   218 nm
(c)   436 nm

### QUESTION 5**

The person sees that there is destructive interference of reflected light of wavelength 450 nm. What is the minimum thickness t of the oil film?

(a)   155 nm
(b)   225 nm
(c)   310 nm

### QUESTION 6*

This and the next three questions concern the following situation:

Which one of the rays for the converging lens shown is not correct?

(a)   A
(b)   B
(c)   C

### QUESTION 7*

Where does the image form?

(a)   between the lens and the right focal point
(b)   at the right focal point
(c)   to the right of the right focal point

The image is

(a)   virtual.
(b)   real.

The image is

(a)   upright.
(b)   inverted.

### QUESTION 10*

This and the next question are about the following situation:

An object is placed 10 cm in front of a convex mirror whose radius of curvature is 5 cm.

Where is the image located? (Be careful all answers can be obtained from numbers given in the problem.)

(a)   2 cm to the right of the mirror
(b)   2 cm to the left of the mirror
(c)   3.33 cm to the right of the mirror
(d)   3.33 cm to the left of the mirror
(e)   No image will be formed.

### QUESTION 11*

If the tip of the arrow is located 5 cm above the principal axis, how far from the principal axis will the tip of the image be located?

(a)   0.2 cm
(b)   1.0 cm
(c)   5.0 cm

### QUESTION 12*

A light ray exits a tank of water (n = 1.3) into the air (n = 1), as shown to the right. Calculate q. (Look carefully at the angles defined in the mirror.)

(a)   40°
(b)   56.7°
(c)   84.8°

### QUESTION 13*

This and the next three questions concern the following situation:

Three identical converging lenses, each with a focal length of 10 cm, are laid out in a row as shown, each 30 cm apart. An object is placed 40 cm to the left of the first lens.

Where is the image due to just the first lens located?

(a)   13.3 cm to the left of the first lens
(b)   13.3 cm to the right of the first lens
(c)   20 cm to the right of the first lens

### QUESTION 14*

Where is the final image (due to all three lenses) located?

(a)   10 cm to the right of the third lens
(b)   10 cm to the left of the third lens
(c)   20 cm to the right of the third lens
(d)   20 cm to the left of the third lens
(e)   40 cm to the right of the third lens

### QUESTION 15*

The final image is

(a)   upright.
(b)   inverted.

### QUESTION 16*

The final image is

(a)   real.
(b)   virtual.

### QUESTION 17*

This and the next three questions concern the following situation:

Which of the rays drawn above for the diverging lens shown is not correct?

(a)   A
(b)   B
(c)   C

### QUESTION 18*

Where does the image form?

(a)   to the left of the left focal point
(b)   at the left focal point
(c)   between the left focal point and the lens
(d)   between the lens and the right focal point
(e)   to the right of the right focal point

The image is

(a)   upright.
(b)   inverted.

The image is

(a)   reduced.
(b)   enlarged.

### QUESTION 21**

Two identical concave mirrors, each with focal length 10 cm, are set facing each other as shown, 50 cm apart. A bead is placed on the principal axis (shared by both mirrors), 10 cm from the left mirror.

Where will the image of the bead form?

(a)   An image will form 10 cm to the left of the right mirror.
(b)   An image will form 20 cm to the right of the right mirror.
(c)   The only image will form infinitely far away.

### QUESTION 22**

This and the next two questions concern the following situation:

A farsighted person has a near point of 75 cm from her eye.

She wants contact lenses that will let her see objects clearly at a distance of only 25 cm from her eye. Determine the focal length of the contact lenses.

(a)   18.75 cm
(b)   37.5 cm
(c)   75 cm

### QUESTION 23***

Will she be able to see objects clearly at a distance of 30 cm if she uses contact lenses that have a refractive power of 3 diopters?

(a)   yes
(b)   no

### QUESTION 24**

If, instead, she wants glasses that will let her see objects clearly at a distance of only 25 cm from her eye. Determine the focal length of the glasses if the glasses are 2 cm from her eyes.

(a)   17.5 cm
(b)   33.6 cm
(c)   73 cm

### QUESTION 25*

A nearsighted person has a far point of 550 cm. She wants contact lenses that will let her see objects clearly at a great distance. Determine the focal length of the contact lenses.

(a)   -25 cm
(b)   -525 cm
(c)   -550 cm

### QUESTION 26*

A person with a pupil diameter of 2.5 mm views the headlights of a distant car. Assume that the headlights are separated by a distance of 1.2 m, and emit light at just one wavelength of 550 nm. What is the distance of the car from the person if the person can just barely resolve the two headlights?

(a)   4,470 m
(b)   5,500 m
(c)   12,600 m

### QUESTION 27*

This and the next question are about the following situation:

For a wavelength of 440 nm, a diffraction grating produces a 2nd-order bright fringe at an angle of 28°.

What is the slit spacing of the grating?

(a)   937 nm
(b)   1,870 nm
(c)   3,749 nm

### QUESTION 28*

For an unknown wavelength, the same grating produces a 2nd-order bright fringe at an angle of 42°. What is the unknown wavelength?

(a)   308 nm
(b)   314 nm
(c)   627 nm

### QUESTION 29*

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

A double-slit experiment is set up using red light with a wavelength of 633 nm. The slits are separated by a distance of 0.075 mm. The interference pattern is viewed on a screen 1.8 m away from the slits.

What is the distance between two adjacent bright fringes on the screen?

(a)   1.52 cm
(b)   1.69 cm
(c)   3.04 cm

### QUESTION 30**

What is the distance between two adjacent dark fringes on the screen?

(a)   0.76 cm
(b)   1.52 cm
(c)   1.69 cm

### QUESTION 31**

What is the difference in the distance traveled by the rays from the top and bottom slit reaching the third order bright fringe on the screen?

(a)   633 nm
(b)   950 nm
(c)   1899 nm

### QUESTION 32**

A single slit of width 0.075 mm, illuminated by light of wavelength 633 nm, yields a diffraction pattern on a screen 1.8 m away. What is the distance between the central bright fringe and the second order dark fringe on the screen?

(a)   1.5 cm
(b)   1.7 cm
(c)   3.0 cm

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.