### Spring 2003 Physics 102 Hour Exam 3(28 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 28 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 92. The exam period was 90 minutes; the mean was 68.6; the median was 69. Click here to see page1 page2 of the formula sheet that came with the exam.

### QUESTION 1*

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

Two thin lenses are separated by 11 cm. Lens #1 is a diverging lens and its focal length is -2 cm. Lens #2 is a converging lens with 7 cm focal length. An object (arrow) is located 8 cm to the left of lens #1.

If lens #2 were not present, the image formed by lens #1 would be

(a)   4.1 cm to the left of lens #1.
(b)   1.6 cm to the left of lens #1.
(c)   1.6 cm to the right of lens #1.
(d)   3.5 cm to the right of lens #1.
(e)   4.1 cm to the right of lens #1.

### QUESTION 2*

Where is the final image of the pair of lenses?

(a)   7.8 cm to the left of lens #1
(b)   3.7 cm to the left of lens #2
(c)   15.8 cm to the right of lens #2

### QUESTION 3*

The final image formed by the pair of lenses is

(a)   upright relative to the object.
(b)   inverted relative to the object.

### QUESTION 4*

The image due to the pair of lenses is

(a)   real.
(b)   virtual.

### QUESTION 5*

What is the magnitude of the magnification of this lens system?

(a)   0.25
(b)   0.69
(c)   1.17

### QUESTION 6*

A person is standing next to a reflecting pool that is 12 meters wide. The pool is at the base of a building that is 115 meters tall. If the person is 1.3 meters tall, what is the farthest distance from the pool she can stand in order to see the reflection of the top of the building in the pool?

(a)   0.14 m
(b)   0.32 m
(c)   0.57 m
(d)   0.61 m
(e)   0.89 m

### QUESTION 7*

This and the next question are about the following situation:

Consider the spherical mirror with focal point f and center C shown in the figure.

For the object (arrow) shown in the figure, where will the image appear?

(a)   A
(b)   B
(c)   D

### QUESTION 8*

Is the image reduced or enlarged?

(a)   reduced
(b)   enlarged

### QUESTION 9*

A light ray comes in parallel to the principal axis of a spherical mirror. Does the reflected ray pass through the focal point?

(a)   Never.
(b)   It depends on the focal length of the mirror.
(c)   Always

### QUESTION 10*

This and the next question are about the following situation:

A fiber optic line can transport light over long distances by using total internal reflection to reflect the light back into the fiber. The fiber shown has a core (n = 1.67) surrounded by a material of a different index (n = 1.33).

Inside the fiber, what is the maximum angle θ capture the light can have and still undergo total internal reflection?

(a)   θcapture = 31.8°
(b)   θcapture = 37.2°
(c)   θcapture = 43.4°
(d)   θcapture = 48.7°
(e)   θcapture = 54.3°

### QUESTION 11*

If the index of refraction of the cladding material is changed to 1.5, θ capture will

(a)   increase.
(b)   remain the same.
(c)   decrease

### QUESTION 12*

This and the next two questions concern the following situation:

A light beam travels through three different materials along the path shown. The index of refraction of the first medium is n1 = 2.1. Only two angles are measured: θ1 = 35°, and θ3 = 49°.

How does the index of refraction of the first medium n1 compare to the index of refraction of the second medium n2?

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

### QUESTION 13*

What is the value of the index of refraction in the third medium?

(a)   n3 = 1.4
(b)   n3 = 1.6
(c)   n3 = 1.8

### QUESTION 14***

What is the minimum value of n2 so that light passes through the third medium?

(a)   n2 = 1.1
(b)   n2 = 1.2
(c)   n2 = 1.3

### QUESTION 15**

A thick lens and a thin lens have the same focal length. How do their indices of refraction compare?

(a)   The index of refraction of the thin lens is larger than that of the thick lens.

(b)   The index of refraction of the thin lens is smaller than that of the thick lens.

(c)   The index of refraction does not affect the focal length of the lenses.

### QUESTION 16*

This and the next question concern the following situation:

With unaided vision your professor can focus only on objects which lie at distances between 3.0 meters and 0.5 meters.

Which type of lens is needed to allow him to see objects beyond 3 meters?

(a)   converging
(b)   diverging

### QUESTION 17**

What power lens does the professor need in his glasses to be able to read a book 0.25 meters in front of his glasses? (Assume the distance between his glasses and his eyes is 0.02 m.)

(a)   | P | = 4.1 diopters
(b)   | P | = 1.9 diopters
(c)   | P | = 0.50 diopters

### QUESTION 18*

This and the next question concern the following situation:

Intense white light is incident on a diffraction grating with 500 lines/mm.

What is the angular separation between violet (400 nm) and red (700 nm) first-order spectra?

(a)   8.95°
(b)   13.5°
(c)   21.1°

### QUESTION 19**

What is the highest order for which the complete visible spectrum (400 nm - 700 nm) can be seen?

(a)   1
(b)   2
(c)   3

### QUESTION 20**

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

Two thick glass plates (n = 1.5) are stacked at an angle, as shown in the picture below. The space between the plates is filled with air (n = 1.0). Light of unknown frequency is incident on the plates, and the first bright spot is observed where the plates are separated by a distance of 1.7 × 10-7 m.

Calculate the wavelength of the incident light. (Be careful all of these wavelengths will give bright or dark spots at that distance!)

(a)   λ = 340 nm
(b)   λ = 453 nm
(c)   λ = 680 nm

### QUESTION 21**

If the space between the blocks is filled with water (n = 1.33), the light intensity at the place where the plates are separated by 1.7 × 10-7 m is now

(a)   still a maximum.
(b)   a minimum.
(c)   neither a maximum nor a minimum.

### QUESTION 22**

Calculate the separation between the plates for the first bright spot, when there is water (n = 1.33) between the plates, and the incident light has wavelength 550 nm.

(a)   103 nm
(b)   140 nm
(c)   185 nm

### QUESTION 23*

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

Monochromatic light (λ = 550 nm) is incident on two slits separated by a distance 1.3 × 10-4 m. Bright fringes are observed on a screen at an unknown distance D from the two slits. The separation between two adjacent bright fringes is 2.5 × 10-2 m.

Calculate the distance D from the slits to the screen.

(a)   D = 5.9 m
(b)   D = 11.8 m
(c)   D = 13.7 m

### QUESTION 24**

If a third slit is made 1.3 × 10-4 m below the bottom slit, the intensity of the light 2.5 × 10-2 m above the central bright fringe will

(a)   increase.
(b)   remain the same.
(c)   decrease

### QUESTION 25*

If the green light (λ = 550 nm) is replaced by red light (λ = 700 nm), the separation between the bright fringes will

(a)   increase.
(b)   remain the same.
(c)   decrease.

### QUESTION 26***

This and the next question are about the following situation:

The waves from a radio station can reach a radio via two different paths as shown in the diagram to the right. One is a straight line path, a distance of 30 km. The other is by bouncing off a cloud midway between the transmitter and the receiver.

Find the minimum height (h) of the cloud that will produce destructive interference between the direct, and reflected waves. The wavelength of the wave is 400 meters. You may assume that there is no phase change upon reflection at the cloud.

(a)   h = 1730 m
(b)   h = 2140 m
(c)   h = 2390 m
(d)   h = 2830 m
(e)   h = 3520 m

### QUESTION 27**

If the cloud were at a height h/2, the signal received at the radio would

(a)   increase.
(b)   remain the same.
(c)   decrease.

### QUESTION 28**

You have two converging lenses that you can use as magnifying glasses. Lens #1 has a focal length f1 = 7.0 cm and lens #2 has a focal length f2 = 15 cm. Which lens can produce the greater magnification?

(a)   Both lens #1 and lens #2 can produce the same maximum magnification.
(b)   Lens #1.
(c)   Lens #2.

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.