Announcements 3/18/11

1. Announcements 3/18/11 • Prayer • Term project progress report due tomorrow night! See website for details. • Exam 2 graded. Median = 90.5, medan = 83.0. • Still missing slinkies from a couple of you. • I’ll be out of town Mon & Wed of next week. Dr. Peatross and Dr. Durfee will substitute • Regular office hours from now on (…except for next week Mon & Wed, because I’ll be out of town.)

2. Thought question • Which will look bigger* to you, a 1 m tall object that’s 5 meters away from you, or a 10 m tall image that’s 50 meters away from you? • 1 m tall object • 10 m tall image • same * In the sense that it takes up more of your field of view

3. Reading Quiz • Which of the following is NOT true of angular magnification? • It is more useful than the absolute magnification when discussing telescopes • It is more useful than the abs. magnification when discussing magnifying glasses • It is given by the equation m = -q/p • The effective distance of the unmagnified image from the eye is 25 cm for a magnifying glass and nearly infinite for a telescope • It is likely to show up on an exam. m = q/q0 … where q0 = “the best you can do without magnification”

4. “Colton picture” r q q (in radians) = (section of arc)/r Quick writing • You are looking at an ant, h = 1 mm. What is the maximum viewing angle you can use to look at the ant, without any lenses?

5. Magnifying Glass • The setup: f = 10 cm • Where would you like the image to be? • Let’s pick q = 50 cm. (This would generally be given in problem.) • What is m? (m = q/q0) • What is q? • What is q0? Answers: q = 6h/50 rad q0 = h/25 rad m = 3 Note: using formulas from book… mmax = 3.5 (for q = 25 cm) mmin = 2.5 (for q = infinity)

6. “Colton picture” r q q (in radians) = (section of arc)/r Quick writing • You are looking at the planet Mars, “h” (diameter, really) = 3.4  106m. The planet, as you are looking at it, is 2.5  1011 m away (this changes from month to month based on the relative positions of Mars and Earth). What is the maximum viewing angle you can use to look at Mars, without any lenses?

7. Telescope These focal spots should essentially overlap (not shown properly in this figure) • The setup: • Given details of setup, what is m? (m = q/q0) • What is q0? • What is q? “Colton picture” for q Answers: q = foh/(rfe) q0 = h/r m = fo/fe

8. triangle: q (rad) = (intermed. height)/fe fe q If intermediate image were formed exactly at the focal point of the eyepiece, final image would be at . As it is, it will just be very far away. image Regardless of how far away it is, though, the angle is given by the blue ray. “Colton picture” for q r fo Because Mars is so far away, image is formed at the focal spot (essentially) Height of image = hfo/r (from M = -q/p)

9. Compound Microscope • I really disliked the book’s somewhat arbitrary “overall magnification” = Mobjective meyepiece because it mixes absolute magnification with angular magnification (but apparently everyone does it that way) • Not on reading assignment, not on HW, not on exam, not especially interesting… let’s not bother with. Onward!

10. Chapter 37! • Interference effects • I.e. now returning to wave nature of light, instead of the ray approximation • Two mathematical facts we will use:

11. Interference... A single source

12. Interference... Two sources

15. intensity screen here Double slit experiment aka “Young’s Double Slit” • Exactly the same as the two speaker demo • Goal: what’s the shape of that curve? How can we predict where the maxima & minima will be? min max min max