Physics 102: Lecture 1, Slide 1

Welcome to Physics 102!

• 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

http://www.communicationcurrents.com

Physics 102: Lecture 1, Slide 2

Meet the Lecturer

• ___________________@illinois.edu

• Research:

• ___________________________________

• ___________________________________

• Office Hours: ______________

Physics 102: Lecture 1, Slide 3

Course Format• http://online.physics.uiuc.edu/courses/phys102/fall09/• 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 just after the lecture is given

• First Discussion: __________• First Lab: ____________• Exam dates:________________________

Physics 102: Lecture 1, Slide 4

Physics 102: Lecture 1, Slide 5

Course Philosophy

• Read about it (textbook and prelecture)

• Untangle it (lectures)

• Play with it (labs)

• Challenge yourself (homework)

• Close the loop (discussion/quiz)

The order is important!

Physics 102: Lecture 1, Slide 6

Grading

• Preflights & Lectures 50• Homework 100• Lab (Prelab due at start of lab) 150• Discussion 150

– Take-home quizzes; drop lowest 1

• Hour Exams (3 x 100) 300• Final Exam 250 1000

Physics 102: Lecture 1, Slide 7

Grading Scale

• 950-1000 A+• 920-949 A• 900-919 A-• 880-899 B+• 860-879 B• 835-859 B-

• 810-834 C+• 780-809 C• 750-779 C-• 720-749 D+• 690-719 D• 610-689 D-• <610 F

Physics 102: Lecture 1, Slide 8

Physics 102: Lecture 1, Slide 9

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 10

Physics 101

• Electricity+Magnetism

• Circuits

• Optics

• Modern• Atomic

• Nuclear

• Relativity

Physics 102Content

• Kinematics

• Forces

• Energy

• Fluids

• Waves (Sound)

Macroscopic Microscopic

Physics 102: Lecture 1, Slide 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

Physics 102: Lecture 1, Slide 12

Physics 102: Lecture 1, Slide 13

Conductors and Insulators

Most things are in between perfect conductor / insulator

Q: How do electrons behave in a perfect conductor?

Q: How do electrons behave in a perfect insulator?

Physics 102: Lecture 1, Slide 14

Electroscope (+demo)

• Conduction– Charged rod is brought near scope– Charged rod touches scope transferring some charge– Scope is left w/ same charge as rod

• 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

Physics 102: Lecture 1, Slide 15

Draw: Electroscope conduction & induction

Physics 102: Lecture 1, Slide 16

Physics 102: Lecture 1, Slide 17

ACTS• 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 18

+ -

r = 1x10-10 m

Qp=1.6x10-19 C Qe = -1.6x10-19 C

Coulomb’s Law

• Magnitude of the force between charges q1 and q2 separated a distance r:

F = k q1q2/r2 k = 9x109 Nm2/C2Mag

nitu

de

and

dire

ctio

n

Solve!

• Force on electron in Hydrogen atom

Physics 102: Lecture 1, Slide 19

Coulomb’s LawF = k q1q2/r2 k = 9x109 Nm2/C2

+ -

r = 1x10-10 m

Qp=1.6x10-19 C Qe = -1.6x10-19 C

Solution: F= 2.3x10-8 NMag

nitu

de

and

dire

ctio

n

Physics 102: Lecture 1, Slide 20

Physics 102: Lecture 1, Slide 21

ACT: Coulomb’s Law

• What is the direction of the force on the proton due to the electron?(A) Left (B) Right (C) Zero

• What is the magnitude of the force on the proton due to the electron?

+ -

r = 1x10-10 m

qp=1.6x10-19 C qe = -1.6x10-19 C

F= 2.3x10-8 NF

Physics 102: Lecture 1, Slide 22

ACT

+ --

Positive charge is attracted (force to left)

Negative charge is repelled (force to right)Positive charge is closer so force to left is larger.

A positive and negative charge with equal magnitude are connected by a rigid rod, and placed near a large negative charge. What is the net force on the two connected charges?

A) Left B) Zero C) Right

221

rqkq

F

Physics 102: Lecture 1, Slide 23

ACT: Induced Dipole

1) Nothing

2) Attracted to charged sphere.

3) Repelled from charged sphere.

• An uncharged conducting sphere is hung next to a charged sphere. What happens when the uncharged sphere is released?

Physics 102: Lecture 1, Slide 24

Physics 102: Lecture 1, Slide 25

Draw what happens:

Physics 102: Lecture 1, Slide 26

ACT: Induced Dipole

1) Nothing

2) Attracted to charged sphere.

3) Repelled from charged sphere.

• An uncharged conducting sphere is hung next to a charged sphere. What happens when the uncharged sphere is released?

Physics 102: Lecture 1, Slide 27

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

Physics 102: Lecture 1, Slide 28

Prior to next lecture….

• Do your prelecture and preflight before 6:00 AM on the day of lecture.