1. Welcome to Physics 102! Please turn cell phones off
Electricity + Magnetism
(at the heart of most processes around us:
…in atoms & molecules; living cells)
Optics
Atomic Physics
Nuclear Physics
Relativity
Please turn cell phones off
Physics 102: Lecture 1, Slide 1

2. Meet the Lecturer Yann Chemla ychemla@illinois.edu Research:
Biophysics
see
Office Hours: Monday 11-12, Loomis 161
Physics 102: Lecture 1, Slide 2

3. When ing me:
must be sent from UIUC account (no Gmail, Yahoo, etc.)
Subject line should begin with “Physics 102 question:”
Message should contain:
student’s full name, netID, discussion section, TA name
Questions about physics:
Do not use , use office hours (see course website)
Before ing:
Verify information is not already on the course website
Physics 102: Lecture 1, Slide 3

4. Course Website
Daily Planner
what you should be doing and when you should be doing it
Course Description
Required Materials
Be sure to register your I-Clicker prior to lecture
Lectures
posted after the lecture is given
First Discussion: See website
First Lab: See website
Exam dates: See website
Go over Daily Planner, Course Description, Lectures
Physics 102: Lecture 1, Slide 4

5. Course Philosophy Read about it (textbook and prelecture)
Untangle it (lectures)
Play with it (labs)
Challenge yourself (homework)
Close the loop (discussion/quiz)
Lectures M,W
HW due 8 AM Tuesday the following week
Disc Tues-Wed, the week following the lecture
Quiz: due two days after Disc
The order is important!
Physics 102: Lecture 1, Slide 5

6. Grading Preflights & Lectures 50 Homework 100
Lab (Prelab due at start of lab) 150
Discussion
Take-home quizzes; drop lowest 1
Hour Exams (3 x 100)
Final Exam
1000
Key to doing well is keeping up with the volume of work. Stuff comes very fast in this course. Lots of new concepts. You need to work hard and often to keep up.
Physics 102: Lecture 1, Slide 6

7. Prelectures & ACTS Do it! Answer preflights 50/1000 points
1 point for honest attempt at preflight.
1 point for using clicker in lecture (ACTS)
2 points/lecture x 25 lectures = 50 points
Note that there are 28 lectures, so you have some free ones
Register I-Clicker before lecture
Physics 102: Lecture 1, Slide 7

8. ACT: iClicker test Let’s switch to “BB” frequency:
hold the power button for 2 seconds (blue light flashes)
push B twice (green light confirmation)
Let’s take a poll. What is your major?
A) pre-med
B) biology (MCB or IB), non pre-med
C) other
D) undecided
iClicker registration problems? Contact me
Physics 102: Lecture 1, Slide 8

9. Content Physics 102 Physics 101 Macroscopic Microscopic
Prerequisite!
Physics 102
Physics 101
Macroscopic
Microscopic
Electricity+Magnetism
Circuits
Optics
Modern
Atomic
Nuclear
Relativity
Kinematics
Forces
Energy
Fluids
Waves (Sound)
There’s a rumor that physics 102 is harder than physics 101…..
Physics 102: Lecture 1, Slide 9

10. Electric charge & Coulomb’s Law
Physics 102: Lecture 01
Electric charge & Coulomb’s Law
Physics 102: Lecture 1, Slide 10

11. Origin of Charge Charge is an intrinsic property of matter Two types:
Positive Charge: e.g. protons
Negative Charge: e.g. electrons
Opposite charges attract. Like charges repel.
The electric force is what holds stuff together
Atoms are neutral
Negatively charged electrons “orbit” around positively charged central nucleus
Start by asking if electric force is so large, why don’t we ever feel it?
Copper and wood both made of atoms, both have positive and negative charges, but are electrically very different. Why?
Physics 102: Lecture 1, Slide 11

12. Conductors and Insulators
Q: How do electrons behave in a perfect conductor?
Q: How do electrons behave in a perfect insulator?
Copper and wood both made of atoms, both have positive and negative charges, but are electrically very different. Why?
Most things are in between perfect conductor / insulator
Physics 102: Lecture 1, Slide 12

13. Electroscope (+demo) Conduction Charged rod is brought near scope
Charged rod touches scope transferring some charge
Scope is left w/ same charge as rod – + +
+ charge +
+ charge
Do the demo first, then show the visualization. Comment on how electroscope works. It’s like VandeGraaff and hair standing on end.
Physics 102: Lecture 1, Slide 13

14. Electroscope (+demo) Induction Charged rod is brought near scope
Scope is briefly grounded allowing charge to flow on (or off) scope
Scope is left w/ opposite charge as rod – + – + –
- charge
Do the demo first, then show the visualization. Comment on how electroscope works. It’s like VandeGraaff and hair standing on end.
Physics 102: Lecture 1, Slide 14

15. ACTS A) positive B) zero C) negative A) positive B) zero C) negative
Set your iClicker
Frequency to “BB”
A negatively charged rod is used to charge an electroscope by induction. What is the resulting net charge on the electroscope?
A) positive B) zero C) negative
If the conducting electroscope were replaced by an insulating ball and then charged by induction as above, what would be the net charge on the ball.
A) positive B) zero C) negative
Physics 102: Lecture 1, Slide 15

16. Coulomb’s Law Force between charges q1 and q2 separated a distance r:
“Coulomb constant”
Magnitude
“Permittivity of free space”
Or:
Magnitude – take absolute value sign for charges, only positive sign
Direction
Opposite charges attract, like charges repel
Physics 102: Lecture 1, Slide 16

17. Example
Coulomb’s Law
What is the magnitude of the force on the proton due to the electron in hydrogen?
F = k q1q2/r2 k = 9x109 Nm2/C2 + -
r = 1x10-10 m
Qp=1.6x10-19 C
Qe = -1.6x10-19 C
Calculate force on electron due to proton
Magnitude
Physics 102: Lecture 1, Slide 17

18. ACT: Coulomb’s Law
Set your iClicker
Frequency to “BB”
What is the direction of the force on the proton due to the electron?
(A) Left (B) Right (C) Zero
What is the direction of the force on the electron due to the proton? + -
r = 1x10-10 m
qp=1.6x10-19 C
qe = -1.6x10-19 C F
Physics 102: Lecture 1, Slide 18

19. Electric dipole –Q H O = = +Q
A positive and negative charge of equal magnitude separated by a (usually small) distance
Ex: water –Q H O d+
2d- – = = +
Dipole of water is permanent +Q
Physics 102: Lecture 1, Slide 19

20. ACT
Set your iClicker
Frequency to “BB”
An electric dipole is placed near a large negative charge. What is the net force on the two connected charges?
A) Left B) Zero C) Right – + -
Positive charge is attracted (force to left)
This is why water is attracted to ions & why it aligns with respect to ions (depending on charge).
Negative charge is repelled (force to right)
Positive charge is closer so force to left is larger.
Physics 102: Lecture 1, Slide 20

21. ACT: Induced Dipole 1) Nothing 2) Attracted to charged sphere. –
Set your iClicker
Frequency to “BB”
An uncharged conducting sphere is hung next to a charged sphere. What happens when the uncharged sphere is released?
1) Nothing
2) Attracted to charged sphere.
3) Repelled from charged sphere. –
Physics 102: Lecture 1, Slide 21

22. Induced Dipole
An uncharged conducting sphere is hung next to a charged sphere. What happens when the uncharged sphere is released? – + –
1) Negative charge attracts + repels –
Explains why non-polar molecules will also be attracted to ions via induced dipole
2) A dipole is induced in the uncharged sphere
3) Since + is closer, attractive force is strongest
Physics 102: Lecture 1, Slide 22

23. Demo: Induced Dipole
An uncharged conducting sphere is hung between a charged sphere and a grounded sphere and held midway between the two. What happens when the uncharged sphere is released? –
The do VdG demo 1121
Physics 102: Lecture 1, Slide 23

24. Summary of Today’s Lecture
The concept of charge
Conductors and insulators
Coulomb’s Law for the force between charges
Much more on Coulomb’s Law in next lecture
Electric dipoles (permanent & induced)
Physics 102: Lecture 1, Slide 24

25. Prior to next lecture…. Do your prelecture and preflight
before 6:00 AM on the day of lecture.
Physics 102: Lecture 1, Slide 25