Welcome to Physics 102

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Welcome to Physics 102!

• Electricity Magnetism
• Optics
• Atomic Physics
• Nuclear Physics
• Relativity

Please turn cell phones off
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Illini EMS

• www.illiniems.org
• General Mtgs
• Wed. Sept. 3rd 7-10pm, 141 Loomis Lab
• Mon. Sept. 8th 5-8pm, 141 Loomis Lab

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Meet the Lecturer

• Alan Nathan a-nathan_at_illinois.edu
• Research
• Experimental Nuclear/Particle Physics
• Physics of Baseball
• see http//webusers.npl.uiuc.edu/a-nathan/pob
• Office Hours Monday 11-12
• or drop in any time and Ill talk with you if I
  am not otherwise tied up

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Course Format

• http//online.physics.uiuc.edu/courses/phys102/fal
  l08/
• 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
  Wednesday
• Lectures
• posted just after the lecture is given
• First Discussion Tues. Sept. 2
• First Lab Thurs. Sept 4
• Exam dates Monday 9/29, 10/27, 11/17 (7 pm)

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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!
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Grading

• PreflightsLectures 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

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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-

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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 Wednesday lecture

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Physics 101
Content
Physics 102
Macroscopic
Microscopic

• ElectricityMagnetism
• Circuits
• Optics
• Modern
• Atomic
• Nuclear
• Relativity

• Kinematics
• Forces
• Energy
• Fluids
• Waves (Sound)

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Origin of Charge

• Charge is an intrinsic property of matter
• Two types
• Positive Charge Protons
• Negative Charge 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

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Conductors and Insulators
Most things are in between perfect conductor /
insulator
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Electroscope

• Conduction
• Charged rod (either or -) is brought near scope
• Gold leaves repel and fly apart
• Charged rod () touches scope transferring some
  charge, then remove rod
• Gold leaves continue to repel
• Scope is left w/ same charge as rod ()
• Now bring rod closer
• Gold leaves repel more
• Now bring rod closer
• Gold leave repel less

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Electroscope

• Induction
• Charged rod () is brought near scope
• Scope is briefly grounded allowing charge to flow
  on (or off) scope
• Note that earth or ground is one huge
  conductor
• Charge can flow freely to or from ground
• When scope is grounded, negative charge attracts
  from ground to the electroscope. The charge
  remains when the ground connection is removed.
• Result scope is left w/ opposite charge as rod

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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
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Coulombs Law

• Example

• Magnitude of the force between charges q1 and q2
  separated a distance r
• F k q1q2/r2 k 9x109 Nm2/C2
• Force on electron in Hydrogen atom

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Coulombs Law

• Example

• F k q1q2/r2 k 9x109 Nm2/C2

F 2.3x10-8 N
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ACT Coulombs 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?

• Example

F 2.3x10-8 N
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ACT
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
Positive charge is attracted (force to left)
Negative charge is repelled (force to right)
Positive charge is closer so force to left is
larger.
-

-
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ACT Induced Dipole

• 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.

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ACT Induced Dipole

• 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.

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ACT 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 -
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ACT 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 -
2) Since is closer, attractive force is
strongest
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ACT 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?

• 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?

1) Negative charge attracts repels 2) Since
is closer, attractive force is strongest
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ACT Induced Dipole

• 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.

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Summary of Todays Lecture

• The concept of charge
• Conductors and insulators
• Coulombs Law for the force between charges
• Much more on Coulombs Law in next lecture

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Prior to next lecture.

• Read Sections 16.1-6
• Do your prelecture and preflight before 600 AM
  on the day of lecture.

See you Wednesday!