Spring 2000 Physics 102 Hour Exam 3
(32 questions)

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This exam consists of 32 questions; two-choice questions are worth 2 points each, three-choice questions are worth 3 points each, five-choice questions are worth 6 points each. The maximum possible score is 110. When the exam was given, the minimum "A" score was 98; the minimum "B" was 85; the minimum "C" was 71; the minimum "D" was 52. The mean was 86.6; the median was 89. Click here to see formula sheet 1, formula sheet 2 that came with the exam.


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

An unpolarized light source with intensity I0 sits in the middle of the six linear polarizers shown in the figure. The orientations of the transmission axes (T.A.) are given with respect to the thin vertical line for each polarizer. The "left side" and "right side" polarizers are numbered sequentially from the light source outward.

Compare I1L and I1R, the intensity of the light after having passed through only the first polarizers (i.e., between planes "1" and "2" on each side).

(a)   I1L > I1R
(b)   I1L = I1R
(c)   I1L < I1R


Calculate the final intensity, IR, of light seen by the right observer. (Be careful -- all of the choices below can be obtained using numbers in the problem.)

(a)   IR = 0.42 I0
(b)   IR = 0.28 I0
(c)   IR = 0


Now the unpolarized light source is replaced with a horizontally polarized light source with intensity I0.

Calculate IL the intensity of light when it gets to the man on the left.

(a)   IL = 0.25 I0
(b)   IL = 0.125 I0
(c)   IL = 0


If the polarizers on the right side were ordered in reverse (i.e. 3, 2, 1) the intensity observed by the right man would

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


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

The drawing shows a convex mirror with an object in front of it (the solid black arrow). The two-sided gray arrows located at positions A) through E) indicate possible locations (but not size) of the image along the principle axis.

Use ray tracing to locate the position of the image on the principal axis. (Note, these arrows are not meant to indicate the final size or orientation of the image, only the location.) Choose a letter and mark it on your answer sheet.



The image is

(a)   inverted.
(b)   not inverted.


The image is

(a)   real
(b)   virtual


Sunlight hitting a car hood at Brewster’s angle is reflected with horizontal polarization. Which way should the transmission axis be oriented on the lenses to minimize the reflected light?

(a)   vertically
(b)   horizontally


The focal length of a flat mirror is

(a)   zero.
(b)   infinite.


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

A mirror is made by slicing off the top of a spherical aluminum shell that has its inside coated with a shiny reflective surface.

A point light source is placed 1.1 m from the mirror surface, an image of the light will form at a distance 2.36 m in front of the mirror. What is the radius r of the spherical aluminum shell from which the mirror was obtained?

(a)   r = 0.75 m
(b)   r = 1.50 m
(c)   r = 3.00 m


Where should you place the light to form a parallel "searchlight" beam?

(a)   x = 0.75 m
(b)   x = 1.5 m
(c)   x = 3.0 m


Which ray in this diagram is wrong?



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

An object is located to the left of the left focal point of a converging lens (f > 0). The two focal points are equidistant from the lens.

The image is located

(a)   between f1 and the lens.
(b)   between the lens and f2.
(c)   to the right of the f2.


The image is

(a)   real.
(b)   virtual.


The image is

(a)   inverted.
(b)   not inverted.


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

In the figure are shown two lenses. The focal length f1 is unknown, but f2 = 14 cm. The lenses are separated by 25 cm. When an object 1 cm high is located 5 cm in front of the first lens, it produces an image (not drawn) 10 cm to the right of the first lens.

Find f1 the focal length of the first lens.

(a)   f1 = 3.33 cm
(b)   f1 = +10.0 cm
(c)   f1 = -8.33 cm


Find d2 the position the image formed by the second lens, expressed as a distance from the second lens.

(a)   d2 = 130 cm
(b)   d2 = 190 cm
(c)   d2 = 210 cm


What is h2 the height of the image formed by the second lens?

(a)   h2 = 14 cm
(b)   h2 = 28 cm
(c)   h2 = 56 cm


The image formed by the second lens is

(a)   real.
(b)   virtual.


If lens 2 is moved slightly to the right, the image formed by lens 2

(a)   will move to the left.
(b)   move to the right.
(c)   not move.


Light with wavelength l = 550´10-9 m is incident upon two narrow slits separated by a distance s before striking a screen 5.2 meters away. The distance between the central and first bright fringe is 1.3´10-3 m. Calculate s the spacing between the slits. (You may approximate sin(q) » tan(q) » q .)

(a)   s = 0.4´10-3 m
(b)   s = 0.8´10-3 m
(c)   s = 1.6´10-3 m
(d)   s = 2.2´10-3 m
(e)   s = 4.4´10-3 m


This and the next question are about the following situation:

A viewer with near point N = 25 cm is viewing an object 2 cm high both with and without a magnifying lens. The lens has a focal length f = 10 cm, and the figure shows the lens in place next to the eye. When the lens is in place the distance between the lens and the eye can be ignored.

What is the maximum angle q at which the viewer can see a sharp image of the 2 cm object without the aid of the magnifying glass?

(a)   q = 2.6°
(b)   q = 3.4°
(c)   q = 4.6°


Calculate M, the angular magnification produced by the magnifying lens when the object is placed 8 cm in front of the lens.

(a)   M = 1.3
(b)   M = 1.9
(c)   M = 2.8
(d)   M = 3.1
(e)   M = 3.7


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

A light source is located a distance 4 m below the flat surface of water. A ray of light from the source emerges from the water at a horizontal distance 3 m.

Find the angle qa at which the light emerges from the water.

(a)   qa = 30°
(b)   qa = 37°
(c)   qa = 53°


The ray of light reaches the eye of a viewer above the surface of the water. You may assume the apparent light source appears directly above its actual position, as shown in the diagram above. What is D ?

(a)   D = 1.5 m
(b)   D = 2.3 m
(c)   D = 2.9 m
(d)   D = 3.3 m
(e)   D = 3.5 m


Calculate the minimum distance x from the actual light source, that an observer 4 meters under the water can see total internal reflection of the actual light from the air/water interface.

(a)   x = 6.31 m
(b)   x = 9.12 m
(c)   x = 12.4 m


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

Two thick parallel plates (with index of refraction n = 1.4 and n=1.2) are separated by a distance 160 nm as shown in the figure below. Calculate the wavelength of light l (in vacuum) that will be constructively reflected when illuminated perpendicularly from above for the following situations. (Be careful some of the choices below correspond to destructive interference.)

The gap is filled with air (ngap = 1.00).

(a)   lvacuum = 320 nm
(b)   lvacuum = 380 nm
(c)   lvacuum = 640 nm


The gap is filled with water (ngap = 1.33).

(a)   lvacuum = 426 nm
(b)   lvacuum = 640 nm
(c)   lvacuum = 852 nm


The gap is filled with carbon disulfide (ngap = 1.80).

(a)   lvacuum = 576 nm
(b)   lvacuum = 640 nm
(c)   lvacuum = 1152 nm


This and the next question are about the following situation:

Monochromatic light incident on a single slit of width 0.2´10-3m produces a diffraction pattern on a screen 3.0 meters away. The distance between the first and second dark fringes is 8.5´10-3 m as shown in the figure to the right. In the following you may assume that the angles locating the fringes are small (sinq »  tanq » q).

Calculate l, the wavelength of the light.

(a)   l = 497 nm
(b)   l = 507 nm
(c)   l = 517 nm
(d)   l = 567 nm
(e)   l = 637 nm


The entire apparatus is placed in a tank of water (n=1.33). The spacing Dx on the screen between the first two dark fringes

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


A hawk has a pupil of diameter 7.5 ´ 10-3 m. What is the maximum distance from which it can resolve the head from the hind of a 6 cm white mouse? Assume that the hawk can perceive all the light reflected off the mouse with wavelength ranging from 300 nm to 700 nm.

(a)   527 m
(b)   878 m
(c)   1054 m
(d)   1230 m
(e)   1756 m