Warm-Up Exercise 31

Due 12:15 pm, Wed 7 Nov 2012

Physics 123, Fall 2012

Reading assignment: 36.8-36.10

Which will look bigger* to you, a 1 m tall object that is 5 meters away from you, or a 10 m tall image that is 50 meters away from you? Explain.
* In the sense that it takes up more of your field of view

They are the same--each will have the same vertical angle in your field of view.

Compare the two situations: (1) You are using a magnifying glass to start a fire by focusing the sun's rays onto some straw. (2) You are using a magnifying glass to help you read small print. Qualitatively, what would "p" be for each situation? What would "q" be?

1) p = distance from sun to magnifying glass = very, very large. q = distance from magnifying glass to straw, a positive number. 2) p = distance from book to magnifying glass = much smaller, perhaps ~12 inches. q = distance from magnifying glass to where it "looks" like the words are (behind the glass), a negative number.

Compare these two Wikipedia lists: Largest optical reflecting telescopes and Largest optical refracting telescopes. Which list contains the largest telescopes overall, and why are the largest telescopes all that variety?

The largest telescopes are all reflecting. It's far easier to build a super-large mirror than it would be to create a super-large lens. (Conveniently, the mirror also avoids chromatic aberration.)

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