PHY105

Science for the 21st Century

EXAMINATION #1

September 27, 2000

 

This is a closed book and closed note exam.  Calculators are not allowed.

 

There are 8 questions on this exam; you are responsible for checking that there are not missing pages.  Questions worth 4 or fewer points are short response (a couple to a few sentences) while the 8 and 9 point questions are medium length essay questions. Well-labeled sketches may be useful in supporting your response.

 

Individual questions are worth the number of points indicated. The maximum possible score is 40 points. Your score is based upon the completeness of your answer (respond to the whole question), including supporting points, and the overall clarity of your answer. 

 

If you need more space for an answer, please clearly indicate how your answer is continued elsewhere.

 

Possibly useful formulas and facts (in words and in symbols):

 

 (angular size) = (size of object) / (distance)                   q = L / d

 

(minimum resolvable angular size) = (1.2 ´ wavelength) / (opening) = (1.2 ´ l) / (w)

 

The wavelength of red light is about 7 ´ 10-7 m (that is, about 700 nm).

 

The wavelength of blue light is about 4 ´ 10-7 m. (that is, about 400 nm)

 

 

1.      (a) [1 point] Give a specific example from the first reading (#1: Megamistakes by Schnaars) that shows the difficulty of predicting future technology.

(b) [2 point] State two factors that cause people to be overly optimistic or otherwise make false predictions about the future of technology.

2.      (a) [3 points] Briefly describe the light ray and visual ray theories of vision. Indicate their similarities and differences.

(b) [1 point] How might one determine which of these two theories better describes physical reality?

3.      Three years from now, you have a job working on the broadcast of the 2004 Olympics from Athens, Greece. You are having lunch with your boss, who wants to have athletes wear very small cameras during events. For this purpose, the cameras need to have resolution of 1 cm at a distance of 50 meters, using visible light.
(a) [4 points] Your boss did not take PHY105. Explain to your boss why there is a limit to how small the camera lens can be made and still have sufficient resolution. What is it about light that causes this limit to exist?

(b) [2 points] Your boss is not convinced by your abstract theory. How can you show your boss that this effect really exists, using materials that might be available in a cafeteria?

(c) [3 points + annual salary bonus in 2004] You have now convinced your boss that if the camera lens is too small, it won't have the required resolution. Your boss would like to see a calculation to estimate how small the camera can be made and still be able to have the needed resolution. Set up the calculation. Be clear as to what numbers need to be divided or multiplied by which numbers to determine the answer, so that your boss can use a calculator later to find the answer.

4.       [3 points] The cartoon reproduced below is from the September 25, 2000, issue of The New Yorker. The cat is viewing a distant scene and the scene's reflection in the level water in front of it. Is the reflection drawn correctly? If not, note what part is not drawn correctly. Most importantly, describe the relationship between objects and their reflected image that allows you to determine if the reflected image is drawn correctly.
[3 points] Shown below is a clipping from the September 22, 2000, issue of The Daily Orange. Note the caption above the photo. It may be hard to see, but the student is working from a photograph of himself. Assume that the portrait copies the appearance of the photograph. Is the portrait being drawn actually a mirror image of the artist? (Compare what a camera sees with a mirror image.) Justify your answer, clearly stating the relationship between objects and their mirror image and how you use this relationship to answer the question.

5.      [3 points] Engineers and scientists are looking into methods for making the ride on an airplane quieter for the passengers. One method that is being studied is to install speakers in the airplane cabin and have them make noise by sending a carefully constructed signal to the speaker. Explain how sound producing speakers could possibly make it quieter in the airplane cabin. Make clear what physical principle (that can be applied to sound) you are using.

6.      (a) [3 points] White light is a mix of pure colors. When this light passes through a prism (when the prism is at the right angle), the light is deflected AND it no longer appears simply white, since you can see the pure colors separately. What causes the light to be deflected and separated? (Describe what happens to the light as it passes through the prism and how it depends on wavelength.)

(b) [3 points] When a red and a green laser shine onto a white Ping Pong ball, the ball can appear yellow. Explain what you see when you look through a prism at the ball and why you see what you see (you do not need to explain in detail why the ball looks yellow to the human eye.

 

7.      [8 points - This is an essay question on color mixing and vision. Please take care to answer each of these sub-questions in your essay, perhaps drawing a line through the question when you address it in your essay.]
If you mix yellow and blue paints (or overlap yellow and blue filters) in roughly equal amounts, typically what color does your eye perceive? If you mix yellow and blue light, what color can they produce (as seen in your lab and in lecture)? What do we call these two types of color mixing (match the term with each example)? Why do these examples produce these two results? [This last subpart is the longest - make sure to include a discussion of how to determine what color the human eye perceives and explain the perceived color for these two examples.]

 

8.      (a) [1 point] Lucretius believed in which theory of vision (give a one word name)?

 (b) [1 point] Briefly describe, in a couple of short sentences, the concept of vision provided by this theory.

 (c) [2 points] Describe an observation that supports this theory and describe an observation that contradicts this theory, using a brief sentence or two, each.