PHY 242 Laboratory for 11/18/99

Yes, it really is time for Exam III. It will take place during the lab period on Thursday, Nov 18. It will consist of 6 to 8 problems and cover Chapters 33 through 37. Here are the usual warnings and disclaimers....

Below are a few sample problems from a previous exam (1992). You are responsible for all material covered in lecture and homework assignments. DO NOT ASSUME that a subject not covered in the sample exam below will not show up on Thursday's exam!

During the exam, you will be provided with an equation sheet. You will be allowed to use only the equations on the sheet, or others that you derive from those on the sheet. I would suggest that you create your own equation sheet from the equations in the summary at the end of each chapter and use only that when trying the problems below. Resist the temptation to simply look for a similar problem in the text or notes (the standard "get the homework done" technique). That will better prepare you for the exam. If you can't solve the problems, come see me. And don't wait until Wednesday night!!

Sample Physics 242 Exam III

1. Chicago's WGN transmits at 50 kW and is received by a television antenna in Indianapolis, 300 km away. What is the radiation intensity (assume isotropic) and what is the rms electric field at the antenna in Indy?

2. A light ray is incident upon a 50-50-80 plastic prism (n = 1.2) making an angle of 40 ⁰ to the normal. Determine the complete path of the ray, labeling all angles in the diagram.
   

3. An object is placed between two plane mirrors which meet at an angle of 30^o as shown. Carefully sketch the first four images formed. Using rays or perpendiculars, indicate how these images are formed.

   

4. You are designing a movie projector using a single convergent lens. The film is 70 mm wide. The screen is to be 30 m from the lens and you want the image to fill the entire 7 m width of the screen. What focal length of lens should you use and how far should it be from the film?
   

5. Sketch a diagram of either a telescope or a microscope. Show the object and the location of all focal points and images.

6. An object is located 30 cm left of a convergent lens of focal length 10 cm. A divergent lens of focal length 20 cm is located 5 cm to the right. Fully describe all images and draw a ray diagram for the first image only.
   

7. A thin layer of oil (n = 1.4) floats on the surface of a lake (n = 1.33 for water). At noon, the reflected sunlight from the oil looks bluish. Estimate the minimum thickness of the oil layer.