PH300 Modern Physics SP11 Charles Baily

1

PH300 Modern Physics SP11 Charles Baily

1/13 Day 1: Why are we here…? What’s this class about ?What do we need to do ? How do we plan on doing it ?Review some math…

Quantum Mechanics is the greatest intellectual accomplishment of the human race. - Carl Wieman, Nobel Laureate in Physics, 2001

2

Today

• Introduction• Why the class is as it is• Structure of the class• Lots of information…• Posted on the Web:(contact info, syllabus, course calendar and

deadlines, pre/post-class lecture notes, etc…)

http://tinyurl.com/PH300SP11

3

PH300 Course InformationLecture: TR 9:30 – 10:45am Room: MH220

Instructor: Charles Baily baily@colorado.eduOffice Hours: By appointmentProblem-Solving Sessions: Tuesdays 12:00 – 2:00pm (tentative)

Physics Library – MH325Homework Due: Thursdays, beginning of class.

Course Website: http://tinyurl.com/PH300SP11Textbook: Thornton & Rex, Modern Physics, 3rd edition (2006)Some additional outside readings (available online)

4

Grading• In-class & online participation (10%)

– Participation only • Daily clicker participation, some in-class activities.

– Graded • Reading quizzes, occasional graded clicker question

• Homework (40%) (most of learning, collaboration helps)– Weekly online (numeric/multiple-choice) and written homework.– Weekly feedback, worth one point of homework extra credit.

• Exams (50%) – (30%) Three midterm exams: In-class, dates 2/8, 3/29, 4/26– (20%) Final, date TBA

Note: Total in-class and weekly homework is a MAJOR part of gradeGrade depends on showing up for class and doing homework.

1 midterm grade dropped if all3 exams attempted

one free week HW credit

(2 “free” days credit)

5

Put your name and contact information on your clicker!

On-Off Button (keep on during class)

Power Indicator (lighted when on)

Low Battery Indicator (<10 h left) replace 3 AAA batteries before next class

Vote Status Green on for 0.5 sec indicates vote receivedFlashing Red – not received

6

Set up your clicker

• Everyday: swap clicker code to XX• Wait for 1st clicker question to open• Hold down On/Off Switch 4 seconds• Flashing blue light: enter X X• Type in Answer.

you’re set for rest of class period• DO NOT TURN OFF CLICKER FOR CLASS (o.w.

repeat above for any new clicker question)

7

Have you used clickers in a prior class?

• A – Yes• B – No

You are NOT locked in to your first choice. Final answer entered will be

the one recorded.

8

Why are you in this class?

9

What will be covered in PH300?Special Relativity:What happens when things go really fast?

Quantum Mechanics:What happens when things get really small?

10

Topics in Special Relativity

• Classical physics before Einstein• Simultaneity• Time dilation and length contraction• Geometry of “spacetime”• Momentum, energy, and “E = mc2”

11

What is Quantum Mechanics?

Pre quantum-understood why stuff falls (gravity), a little about properties of electric and magnetic fields, gases.

Quantum- understand underlying behavior of everything youare likely to see or experience in your lifetime! • properties of all basic materials• properties of light and other EM radiation• how light interacts with matter• basis for all modern technology, etc.

12

PH300 Modern Physics – Spring 2011

Overall course goal:

Every student learn everything!

13

PH300 Modern Physics – Spring 2011

General goals: • Understand how modern physics has changed how we

view the world around us.

• Understand the microscopic origin of the behavior of materials-- in the world and technological applications.

• Emphasis on understanding and applying concepts.How do you know? Why does it matter?

• Some emphasis on interpretation What does this all mean?

"I think quantum mechanics is an interesting subject."

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1AGREE NEUTRAL DISAGREE

Pre-Instruction Average(6 Semesters 2130)

Post-Instruction Average(5 Semesters 2130)

Post-Instruction2130FA10

2130 – 6 SEMESTERS

15

Traditional Model of EducationInstruction viatransmissionIndividual Content (e.g. circuits)transmissionist

16

1. People understand concepts by seeing, discussing, and applying them, not by passively listening to explanations.

2. Understanding physics (& solving problems that develop understanding) is a learned skill, like golf or playing basketball or violin. Takes time, effort, and practice. Research says better retention if sustained effort

rather than cramming.3. People learn best by sharing and getting feedback on their thinking

-- Student-student more often than student-faculty.4. Students learn most when they take the responsibility for what is learned.

Physics is not a collection of facts

It is way of thinking. Only you can teach yourself to think! Analyzing, applying concepts, solving problems.

Guiding principles: (basis for how course is run)

17

We provide you with opportunities to help you learn.Content, problems, simulations, guidance, organization.

Learning only comesas a result of your effort!

Model for learning in PH3001. Read pre-class notes – introduce ideas and terms.2. Analysis and discussion in class – explore, develop basic ideas and

understanding.3. Master and retain ideas through use in extensive HW (4-6 hrs/wk)(collaboration good, but submit own work)

18

Collective Work vs. Independent Work

What is authorized:- working with others to make sense of questions- collectively sorting out the answer (explaining reasoning)- writing up your own solution in your own words

What is NOT authorized:- telling students the answer- representing someone else’s work as your own

Group Work Encouraged(in fact, hopefully, necessary)

19

Best education is one-on-one examination of thinking and immediate feedback.Learn to do for each other-- win-win situation, you both learn more. Main learning time!

Problem Solving Sessions

Regular Weekly Hours (Starts next week)

Tuesdays: 12:00-2:00 pm(subject to change; see course website)

Location: Physics library – MH335

20

21

What is your background inmathematics?

My last completed mathematics course:

A) 2nd semester calculusB) 3rd semester calculusC) Linear algebraD) Differential equationsE) Higher math course…

22

exp( ) cos sini i

A) I know exactly what this equation means.B) I think I know what this equation means.C) I’ve seen it before but am not sure what it means.D) I’ve never seen this equation before.

Euler’s Equation

23

Some math to reviewComfort with algebra:

e.g.Given at = b and cx + dt = f and the values of a, b, c, d and f, but you don't know the value of t or x, solve for the value of x.

• solve for unknown t in terms of known quantities: • put that into the other equation:

• Then solve for x:

t ba

cx d ba

f

x 1c

( f d ba

) fc

dcba

24

Exponential notation

You should be comfortable with exp. notation3

4

4 10 ?10

Note: e = 2.72exp( )xe x

exp( )exp( ) exp( )x y x y

exp( ) exp( )exp( )

x x yy

exp(0) 1

25

Basic calculusDerivatives

z = ax3 + bx + c, then

Integrals:

?dzdx

cos( ) ?d xdx

( ) ?atd edt

20

sin cos ?L x x dx

L L Hint u = sin(x/L)

du = cos(x/l)1/Ldx

?ate dt

26

Complex numbersi2 = -1

z = x + i y (x is real part; y is imaginary part)

z* = x - i y complex conjugate; replace “i” with “-i”

Magnitude of z: |z|2 = z*z

= (x - iy)(x + iy) = x2 + ixy – ixy + y2 = x2 + y2

Special result (from Taylor expansion): ei = cos () + i sin()

i 1

27

Differential equations

2''( ) ( )y x k y x

( ) cos( ) sin( )y x A kx B kx ( ) exp( ) exp( )y x A ikx B ikx ( ) exp( ) exp( )y x A kx B kx

What is the most general solution to the differential equation:

A) B) C) D) A & BE) A & B & C

28

2

2''( ) cosdy x kxdx

sin( )d k kxdx

2 2 cos( ) = ( )k kx k y x

2''( ) ( )y x k y x

Differential equations

Function is negative, curvature is positive

Function is positive, curvature is negative

29

Differential equations

2''( ) ( )y x k y x

( ) cos( ) sin( )y x A kx B kx ( ) exp( ) exp( )y x A ikx B ikx ( ) exp( ) exp( )y x A kx B kx

What is the most general solution to the differential equation:

A) B) C) D) A & BE) A & B & C

30

exp(-kx)

Slope of function is always increasing (becoming less negative).

Differential equations

What is the most general solution to the differential equation:

2''( ) ( )y x k y x