Welcome to Welcome to Physics 106!Physics 106!

Light, Perception, Photography, and Visual

Phenomena

Webpage for the CourseWebpage for the Course

www.physics.umd.edu/courses/Phys106/xji

WarningWarning

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 JiOffice: Room 2102, Physics Building

Phone: 301-405-7277

Email: xji@physics.umd.edu

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?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 Please do not walk out of the classroom of the classroom

in the middle of a lecture!in the middle of a lecture!

Physics 106

An Outline of Physics 106An Outline of Physics 106

Part I: Geometric Optics and Simple Applications– Fundamental Properties of Light

What is Light? Waves, Electromagnetic Radiations

– Principles of Geometrical OpticsShadows, 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?What is Light?

Why do we see?How fast does light

travel?What is light?

WHY DO WE SEE?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?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?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 (1672-1680), 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 Could Alpha Centauri Support Life?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