Announcements 11/7/12

Announcements 11/7/12 Prayer Term project progress report due Saturday

nighta. Evidence of progressb. Text in body of email, list of group

members, and group members CC’ed on the email

Calvin & Hobbes

From warmup

Extra time on? (nothing)

Other comments?a.What does “subtends” mean? (2 people)

Clicker quiz

Have you tried LearnSmart?a.yesb.no

If you have tried it, how useful has it been? (only answer if you have tried it)

a.Veryb.Moderatec.Slightlyd.Not at all

Summary of Near point vs. Far point

Person A = nearsighteda. Can’t focus on object at infinity b. Use lens to bring object at infinite to image

at “far point”– image distance = negative!

Person B = farsighteda. Can’t focus on object at 25 cm (comfortable

reading distance)b. Use lens to bring object at 25 cm to image

at “near point”– image distance = negative!

From warmup: 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?

a. 1)p is the distance to the sun from the magnifying glass, q is the distance of the magnifying glass to the straw2)p is the distance from the letters to the magnifying glass, q is the distance of the magnifying glass to your eyeVery common answer, but wrong!

Quick writing: what is q for case 2? (talk to your neighbors; click in when you’re ready to answer)

From warmup: 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?

a. They will look the same size. They both are at an angle of arctan(5/1) with respect to the principal axis.

* In the sense that it takes up more of your field of view

“angular size”

Worked Problem What is the angular size of a 0.1 m tall

object that’s 5 meters away from you?

Two methods!

Thought Question Which method should you use?

a. Method Ab. Method B

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?

r

“Colton picture”

(in radians) = (section of arc)/r

Clicker question: Which of the following is NOT true of angular

magnification?a. It is more useful than the absolute magnification

when discussing telescopesb. It is more useful than the abs. magnification when

discussing magnifying glassesc. It is given by the equation m = -q/pd. It is likely to show up on an exam.

m = /0 … where 0 = “the best you can do without magnification”

Magnifying Glass The setup:

f = 10 cm

Where would you like the image to be? Let’s pick q = -50 cm. (q would generally be given

in problem.) What is m? (m = /0)

a. What is ?b. What is 0?

Answers: = 6h/50 rad 0 = h/25 radm = 3

Note: using formulas from book…mmax = 3.5 (for q = 25 cm)mmin = 2.5 (for q = infinity)

Quick writing

You are looking at the planet Mars, “h” (diameter, really) = 3.4 106 m. 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?

r

“Colton picture”

(in radians) = (section of arc)/r

Telescope

The setup:

Given details of setup, what is m? (m = /0)

a. What is 0?

b. What is ?

These focal spots should essentially overlap (not shown properly in this figure)

“Colton picture” for

Because Mars is so far away, image is formed at the focal spot (essentially)

fo

Height of image = hfo/r (from M = -q/p)

r

fe

image

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.

Regardless of how far away it is, though, the angle is given by the blue ray.

triangle: (rad) = (intermed. height)/fe

Answers:0 = h/r = foh/(rfe)m = fo/fe

From warmup

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?

a. Reflecting is much larger. The glass in large refracting telescopes would sag so they use mirrors instead since they can support the back of them.

b. reflecting telescopes are larger. this is because there are no aberration issues with reflecting telescopes so they can give clearer images.

c. Also (my answer): only need to polish one side—saves a lot of money

Reflecting Telescope

A “Newtonian Reflector”

http://lcogt.net/en/book/reflecting-telescopes

Incoming Light

Mirror

CurvedMirror

eyepiece lens

Compound Microscope

http://en.wikipedia.org/wiki/Microscope

I really dislike the eqn: “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!

Chapter 37!

Interference effectsa. I.e. now returning to wave nature of

light, instead of the ray approximation

Two mathematical facts we will use:

cos2

ix ixe ex

sin

2

ix ixe ex

i

Interference... Interference...

A single source

Next few slides: credit Dr. Durfee

Interference... Interference...

Two sources