Geo 406 Lecture 01 - Introduction, Light
Reading: p. 3-7, 16-24
next: p. 7-15
Goals
Learn goals of course
Learn organization of course
Take photos
Schedule extra hour
Learn about light and particles, waves, and rays
Learn basics of microscope
About me
History
Research interests
Teaching experience
Good & bad aspects of new instructor - enthusiasm, but mistakes
Demo (why optical mineralogy)
Sed rock - what is the diagenetic history?
Met rock - what was the maximum temperature this rock experienced?
Ig rock - was the magma chamber that these plagioclase crystals grew in
strongly convecting or not?
Demo (what will you learn)
Calcite - double refraction
Iolite - pleochroism
Quartz wedge & polars - interference
How do polarized sunglasses work?
Goals of course
Learn to identify minerals in thin section - lab stuff
Learn how the interaction of light and crystals produces features we
observe in thin section - lecture stuff
Learn about mineralogic and petrologic features observed in thin section -
both lab & lecture
Nature of class
The are two groups – some have had some optical, other have not.
There will be a fair amount of review for those from last quarter’s 306.
Syllabus
Everything is subject to change, especially given that this is the first
time I've taught this class in this format with this many students.
Web site
All info is posted online.
Can check scores / grades interactively
Blackboard
Used only for email.
You can send email to the class via blackboard as well. Works like a
discussion group.
Grading
Mainly based on tests & labs - few homeworks
Quizzes probably every class - provides attendance/promptness score as well
Some will be dropped
Attendance
Really important
Better late than never
Lecture and labs
Probably mingled, although I'll try to assign labs on Tuesdays
Early in Quarter - focus is on lectures
need to get basic info across
Later - focus on labs
email
I must be able to contact you via email!
See syllabus for how.
I will send out a small quiz over email this weekend.
Feedback
Very important - responsibility to future students
Think of the best teachers you've ever had. Most started out much worse
and got better by students telling them what worked and what didn't
This is my second time teaching this course, and first time teaching it
with a class this size
I appreciate comments in person, via email, and via the anonymous comments
form on the website
Questions
Ask lots!
Small class - lots of discussion
Organization
Everybody get somebody’s phone number or email.
Light
Nature
Particle / wave
In this course, we will be mostly concerned with the wave aspects
Transverse (like a phone cord) or longitudinal (like sound) wave?
Demo: Light with polars. Put in line, source, polar EW, polar EW, eyeball
If light is a longitudinal wave, then there should be no directionality
other than along the wave travel direction
If light is transverse, then there may be cases in which the direction
matters
Some surface waves in earthquakes only vibrate vertically
Show that rotating upper polar changes total intensity of transmission -
proves light is a transverse wave
Polarization
Light has a vibration direction (diagram)
In fact, there are two: the electric component vibrates 90° from the
magnetic component.
In this course, we will ignore the magnetic component
Normal light is really lots of rays of light, each vibrating in a random
orientation - "unpolarized"
By passing light through a special sheet (made up of organic polymers
oriented in a single direction), we remove all components vibrating in
directions other than the orientation of the sheet - "polarized"
Wave features
velocity, v
wavelength, l
frequency, n
n = v/l
Interference
diagram constructive and destructive interference
Speed
3e8 m/s - in vacuum only!
In other substances (air, water, glass, minerals), light travels slower
We can measure speeds in these substances, and come up with a value
representing the amount by which light is slowed in various substances, n = vvacuum/vmedium
n is larger for "slower" substances
n can never be less than 1.0
maximum n ever found? Bose-Einstein condensate
Hwk for Thursday - Look this up and find or calculate n for this substance
n is called the "index of refraction" - we will find out why in
the next lecture
Scope
Your scope is basically a light
source, a polarizing sheet ("nicol" or "polar"), the rock
sample, and another polarizing sheet, with some magnifying lenses tossed in
along the way.
It is the polarization aspects that
primarily distinguish a petrographic microscope from other microscopes.
Read lab and work on it for remainder
of time
use your text as a reference
ask questions, if the text isn't
clear
How to center objectives
Why it matters
more at high power.
don’t want what you’re viewing to leave field of view as you rotate the
stage
1.
Pick feature at center of FOV
2.
Rotate stage 180° and watch where feature goes.
3.
Adjust objective until feature moves halfway back to center
4.
Repeat.