Assign9 - PHY 54! Assignment 9! Summer 2011 Reading: Lenses...

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: Lenses and Mirrors; Applications Key concepts: Focal points and lengths; real images; virtual images; magnifcation; angular magnifcation. 1. Questions about objects and images. a. Can a virtual image be seen on a projection screen? b. Can a virtual image be photographed? c. What is a virtual object? Give an example. 2. Questions about the eye and corrective measures. a. Why is our vision so blurred underwater? How do goggles solve the problem? b. Most eyeglass lenses have a standard convex outer surface (the one furthest from the eye) for cosmetic reasons. Draw a cross section of such a lens that has a negative focal length. c. If you look closely through the eyeglasses at the eyes of the wearer, you can tell whether the person is nearsighted or farsighted. How? 3. Questions about magniFcation. a. The magniFcation of instruments such as a magnifying glass increases when the focal length of the eyepiece is reduced. Why are lenses of focal length shorter than about 5 cm rarely used? b. What is angular magniFcation, and why is it the measure used to describe the power of optical instruments? c. The telescope and microscope both use two positive lenses. Why is the microscope’s magnifying power so much larger? 4. Make a drawing of an overhead projector of the type used in classrooms. Show why, if the speaker is facing the audience and projecting onto a screen behind him, the image of the slide she is reading from is upright and enlarged on the screen. . 5. Questions about focusing. a. To change the focus of a Flm camera using ordinary lenses from a distant object to one closer, how is the distance from lens to Flm changed? b.
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This note was uploaded on 10/19/2011 for the course PHYSICS 54L taught by Professor Thomas during the Summer '09 term at Duke.

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Assign9 - PHY 54! Assignment 9! Summer 2011 Reading: Lenses...

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