Transcript Welcome to Physics 106!

Welcome to
Physics 106!
Light, Perception,
Photography, and Visual
Phenomena
Webpage for the Course
www.physics.umd.edu/courses/Phys106
/xji
Warning
 In
order to meet the CORE lab science
requirement, you must take Physics
107 (the lab course associated with
106) during the SAME semester as
Physics 106. Physics 106 taken alone
does NOT satisfy the CORE non-lab
science requirement!

Instructor: Dr. Xiangdong Ji
Office: Room 2102, Physics Building
Phone: 301-405-7277
Email: [email protected]
Office hours: 11:00am-12:00pm, Mon & Wed

Textbook:
– Seeing the light, by D. Falk, D. Brill, and D.
Stork (John Wiley and Sons, New York,1986)

Objective of the Course:
Have Fun with Physics!

Homework:
Assigned weekly and collected the
following week before class starts.
No late homework!
 Exams:
Two mid-terms:
Friday, Feb.27 & Friday, April 9
Final:
1:30pm-3:30pm, Monday, May, 17
All exams are closed-book!
(missing exam?)
Grades?

Based on the following approximate
percentages:
– Two Midterms: 20% each; Final Exam: 30%
– Homework: 20%
– Attendance: 10%

You do not have to get 90% and above to
get an A!
– 30% students: A
30%: B 30%: C
– 10% student : D&F (score below 40%)
Please do not walk out
of the classroom
in the middle of a lecture!
Physics 106
An Outline of Physics 106

Part I: Geometric Optics and Simple
Applications
– Fundamental Properties of Light
What is Light? Waves, Electromagnetic Radiations
– Principles of Geometrical Optics
Shadows, Reflection, Refraction, Dispersion
– Mirrors and Lenses
– Camera and Photography

Part II: Vision and Color
– Structure and functions of an eye.
– Lightness perception: Processing the image
– What is color? How to mix colors?
– Color perception mechanism

Part III: Wave Optics
– Light as waves: Interference & Diffraction
– Scattering and Polarization
– Holography
– Light in Modern Physics
What is Light?
 Why
do we see?
 How fast does light
travel?
 What is light?
WHY DO WE SEE?

We have eyes!
– But, how do eyes work? There are many
possible reasons that an eye couldn’t see!

There are lights coming into our eyes!
– Where are the lights coming from?
Light sources: the Sun (source of most energy),
Fireflies, Candle Flames,light bulbs
Television Screen,…
Reflected or Scattered light:
from objects like buildings, trees,
clouds, highways, books, your
beautiful face, ….

You don’t see if the light does not go
directly into your eyes even if it just passes
by your nose!
– The sun is still beaming light into the space at
night! (How do you know?) But you don’t see
it directly.

On the other hand…
– We do see light beams from search lights, flash
light, sunlight through foliages. Why do we see
them if they are not directed at us?
– I have a pitch-black object in my hand which
does not scatter any light, but why do you see
it?
HOW FAST DOES LIGHT TRAVEL?

Very Fast!
– There is no delay between turning on a light
and seeing its beam hit a distant object.
– Sound travels one mile/5 sec. But light travels
much faster!
– The speed of light is not infinity!
C = 300,000 km/sec
Or = 186,000 miles/sec
Go around the earth 7 and ½ time in a sec.
How to measure the speed of light?

Galileo Galilei (1564-1642)
– Hired two men stationed on hill tops a mile apart…

First true observation of a time delay due to
light’s travel: Ole Roemer (1644-1710)
While at Royal Observatory in Paris (16721680), he found the eclipses of Jupiter’s moons
appear earlier as the earth moves toward it and
later as the earth moves away.
C=140,000 miles/sec

The speed of light is the fastest speed that
any information can travel! (Einstein)
– How about the latest claim of light being
slowed down and stopped?

The upper limit of the speed is too small!
– It takes millions of years for star lights to reach
us. Some of the stars might be dead already!
– It takes about 20 min for the instructions to
reach Land Rovers on the Mars.
– It takes 3 years for light to reach us from the
nearest star system: Alpha Centauri!
Could Alpha Centauri Support
Life?
Please consult:
http://homepage.sunrise.ch/homepage/
schatzer/Alpha-Centauri.html

First Accurate Measurement of c (~1881)
Albert A. Michelson (1852-1931)
Nobel Prize, 1907

Today, the speed of light is one of the most
accurately measured constants in physics. In
fact, the basic unit of length, meter, is
defined so that
C = 299,792,458 m/s