Fall 2001 Physics 102 Hour Exam 3
(31 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 31 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 118. When the exam was given, the mean was 90.7; the median was 92. Click here to see page1 page2 of the formula sheet that came with the exam.


QUESTION 1**

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 person’s head. Assume for simplicity that the person’s eyes are at the height of the top of his head.

What part of his 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 2**

Which one of the mirrors below (in the absence of the other mirrors) would cause light from a distant source on the left-hand side of the paper to be focused to a point that is closest to the mirror?


(a)   
(b)   
(c)   
(d)   
(e)   


QUESTION 3***

The two lenses shown at right have the same focal length. The index of refraction of lens B is 1.5. The index of refraction of lens A can be:

(a)   2.0
(b)   1.7
(c)   1.5
(d)   1.3
(e)   1.0


QUESTION 4**

When it is in air, a converging (concave) mirror causes rays of light from a distant source to converge to a point that is 8 cm from the mirror. When the mirror and the rays of light are immersed in water, the mirror causes the light to converge to a point that is at a distance from the mirror

(a)   greater than 8 cm.
(b)   equal to 8 cm.
(c)   less than 8 cm.


QUESTION 5*

This and the next two questions concern the following situation:

An object of 5 cm height is at a position 15 cm away from a spherical concave mirror. The radius of curvature for the mirror is 20 cm. The locations of the center of curvature (C) and the focal point (F) are indicated.


How far will the image be from the mirror?

(a)   15 cm
(b)   20 cm
(c)   25 cm
(d)   30 cm
(e)   35 cm


QUESTION 6*

What is the height of the image?

(a)   2.5 cm
(b)   5.0 cm
(c)   10 cm


QUESTION 7*

The image is

(a)   upright.
(b)   inverted.


QUESTION 8*

This and the next two questions concern the following situation:

The object (the arrow) and a diverging lens are positioned as shown in the figure. The locations of the focal points are indicated by F. This figure (but not necessarily any other figure in this exam) has been carefully drawn to scale.

How far will the image be from the mirror?

(a)   A
(b)   B
(c)   C


QUESTION 9*

Is the image enlarged or reduced?

(a)   enlarged
(b)   reduced
(c)   same size as the object


QUESTION 10*

If the object is moved 1 cm toward the lens, how will the image move?

(a)   It will move toward the lens.
(b)   It will move away from the lens.


QUESTION 11*

This and the next three questions concern the following situation:

Two lenses are separated by 11 cm. Lens #1 is a converging lens and its focal length is 4 cm. Lens #2 is also a converging lens with 5 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)   12 cm to the left of lens #1.
(b)   4 cm to the left of lens #1.
(c)   4 cm to the right of lens #1.
(d)   8 cm to the right of lens #1.
(e)   12 cm to the right of lens #1.


QUESTION 12*

Where is the final image of the pair of lenses?

(a)   3 cm to the left of lens #1
(b)   3.5 cm to the right of lens #1
(c)   6 cm to the left of lens #2
(d)   4.5 cm to the left of lens #2
(e)   1.5 cm to the right of lens #2


QUESTION 13**

The final image formed by the pair of lenses is

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


QUESTION 14*

Do rays of actual light converge to create the final image due to the pair of lenses?

(a)   yes
(b)   no


QUESTION 15*

This and the next question concern the following situation:

A ray of red 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 what medium does the light travel the fastest ?

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


QUESTION 16**

If the incident ray of light in the figure is blue (instead of red) and these media have optical properties that are common for media such as glass and water, the blue light will emerge from the interface between n3 and n1

(a)   to the right of where the red ray emerged.
(b)   at the same point as where the red ray emerged.
(c)   to the left of where the red ray emerged.


QUESTION 17*

A ray of light hits a surface of the diamond (n = 2.4) from within as shown. What is the maximum angle F for which there will be total internal reflection of the ray?

(a)   34°
(b)   49°
(c)   65°


QUESTION 18*

This and the next question concern the following situation:

The nearest point at which my friend can read text without the aid of glasses is 250 cm. To read a book held at 30 cm distance, my friend must use eyeglasses.

The eyeglasses should be

(a)   converging lens.
(b)   diverging lens.


QUESTION 19*

What is the absolute value of the focal length to be used for the reading glass?

(a)   29.1 cm
(b)   34.1 cm
(c)   37.1 cm


QUESTION 20*

This and the next question concern the following situation:

An object is placed an unknown distance (x cm) in front of a convex mirror with a focal length f = -5 cm. The locations of the focal point (F) and the center of curvature (C) are shown.


Which one of the following statements is wrong?

(a)   Rays of actual light always meet to form the image.
(b)   The image is always upright.
(c)   The image is always reduced in size.


QUESTION 21**

For what distance x will the image be reduced by a factor of two?

(a)   2.5 cm
(b)   5 cm
(c)   7.5 cm
(d)   10 cm
(e)   15 cm


QUESTION 22*

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

Light with frequency f = 5.5 × 1014 Hz is incident upon two narrow slits separated by a distance 0.8 × 10-3 m before striking a screen 4.2 meters away.

Calculate h, the distance between the central and first bright fringe.

(a)   h = 2.1 × 10-3 m
(b)   h = 2.9 × 10-3 m
(c)   h = 4.3 × 10-3 m
(d)   h = 7.2 × 10-3 m
(e)   h = 8.6 × 10-3 m


QUESTION 23**

A third slit is now placed directly between the first two slits. So the spacing between the three slits is 0.4 × 10-3 m. What happens to the intensity of the light at the original location of the first bright fringe?

(a)   increases
(b)   remains the same
(c)   decreases


QUESTION 24**

The entire apparatus is placed under water. What happens to the distance h between the bright fringes?

(a)   increases
(b)   remain the same
(c)   decreases


QUESTION 25**

This and the next question are about the following situation:

A thin layer of carbon disulfide (n = 1.6) is resting upon two blocks. The first block is made of ice (n = 1.3) and the material of the other is block is unknown. When viewed from above, green light (l0 = 550 nm in air, f = 5.5 × 1014 Hz) constructively interferes off the left side (ice block), and destructively interferes off the right side (unknown block).

What is a possible thickness t of the thin layer of carbon disulfide?

(a)   t = ½ l0
(b)   t = ½ l0 / n1
(c)   t = ¼ l0 / n1
(d)   t = ½ l0 / n2
(e)   t = ¼ l0 / n2


QUESTION 26*

Which of the following materials could the unknown block be made from?

(a)   diamond
(b)   crown glass
(c)   ice


QUESTION 27**

This and the next question are about the following situation:

An inkjet color printer uses tiny dots of red (l = 660 nm), green (l = 550 nm) and blue (l = 470 nm) ink to produce an image. At normal viewing distances, 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
(b)   green
(c)   blue


QUESTION 28**

What is the maximum acceptable dot spacing so that a person with normal, unaided vision (near point 25 cm, far point infinity, pupil diameter 2.0 mm) can just resolve the individual green dots?

(a)   44 µm
(b)   65 µm
(c)   84 µm
(d)   110 µm
(e)   128 µm


QUESTION 29*

This and the next question are about the following situation:

Monochromatic light shines on a diffraction grating with 9600 lines/cm. The first-order maximum occurs at an angle of 33 degrees.

What is the wavelength of the light?

(a)   l = 865 nm
(b)   l = 683 nm
(c)   l = 567 nm


QUESTION 30**

What is the highest order bright fringe (not counting the central fringe) which occurs with this setup?

(a)   1
(b)   2
(c)   3


QUESTION 31**

Light of wavelength 550 nm is incident on two parallel slits which have widths of 600 µm. The intensity on a screen beyond the grating is shown.

The separation between the slits is:

(a)   7 mm
(b)   14 mm
(c)   28 mm