Course Organization

• John Yeazell, jyeazell@austin.utexas.edu• Syllabus • Evening Recitation sections

• Monday session cancelled for Labor Day• Quest• i-Clickers (register on Quest)

What you need to remember from 303K

Vectors����

��+�� �� ∙ ��=|𝐴||��|𝑐𝑜𝑠 (𝜃 )𝜃 |��× ��|=|��||��|𝑠𝑖𝑛 (𝜃 )

Right Hand Rule

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How particles move and are affected by forcesMomentum: ; Newton’s 2nd Law:

Work and Energy:

Clicker Question 1 and . What are and ?

ChoiceA 2BC 3 2D 3

Clicker Question 2 and . What is ?

ChoiceABC 4

Recall:

Use your results to find ChoiceABC

Clicker Question 3 and . What is ?

ChoiceABC 4

Recall:

W ?

Choice Unit vectorABC

aurora borealis

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• Sun spits out Charged Particles (Solar Wind)• Earth’s Magnetic Field extends out into space

and collects charged solar wind.• Charged particles are concentrated at poles• Collisions of these high velocity charges with air

makes the light of the aurora

What will you learn?

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Interaction of Matter and Electromagnetic Fields

Backpacking in Alaska

The interactions between Matter and Electric and Magnetic fields can be explained with just a few equations.

Maxwell equations:

Lorentz force:

More Mathematically …

• Two types: positive and negative

• Like charges: repel

• Opposite charges: attract

• Charge is quantized in units of e

Millikan’s oil drop experiment (1910-1913)

• Point charge: Size is small compared to the distance between it and other objects of interest

• Electric charge is an intrinsic property of the fundamental particles that everything is made of

Point Charges

Q1 Q2

F F

"The magnitude of the electrostatic force between two point charges is directly proportional to the magnitudes of each charge and inversely proportional to the square of the distance between the charges."

The Coulomb Force Law

Charles-Augustin de Coulomb (1736 - 1806)

The Coulomb Force Law

0 = permittivity constant

Force repulsive

1

+

+

2

rF21

Force attractive

+

-

2

r

F21

1

Force on “2” by “1”

Units and ConstantsSI units of electric charge: Coulomb, CConstants:

1/40 = 9x109 N.m2/C2

0 = 8.85x10-12 C2/N.m2 permittivity constante = 1.602x10-19 C1 C = 6.24x1018 elementary charges

Particle Chargeelectron -epositron +eproton +eantiproton -emuon +e or –epion +e or –e or 0neutron 0

Structure of Atom

Nucleus: ~104 times smaller than electron cloud, ~104 times heavier than electron.

Matter consists of atoms1 cm3 : ~1024 atoms

Example: nucleus of the iron atomSize: ~10–15 m, mass: ~10-25 kg

1Å=10-10m

Nucleus charge = +Ze, atom with Z electrons is neutral.

The Concept of Electric Field

Accelerates at 9.8 m/s2 – why?

Accelerates at 1011 m/s2 – why?

There are many possibleconfigurations of charges to produce the observed effect.

There is something in space waiting for a charged particle to interact with it!This virtual force is called electric field.

An electric field created by charge is present throughout space at all times, whether or not there is another charge around to feel its effect.

Electric Field

The Electric field of the Point Charge Q

Force between Charges

Q

q

Electrical Field is convenient tool

��=𝑘𝑄𝑞

|𝑟|2𝑟

𝑟

¿ {𝑘𝑄|𝑟|2 𝑟 }𝑞

��=𝑘𝑄

|𝑟|2 𝑟

turns out to be measurable … so really exists

��=𝑞𝐸

+

+

𝑘=1

4𝜋 𝜀0

Electric Field of Point Charge

+

Spherically Symmetric

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+

Draw the E field for a Negative Charge

_ ��

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E Field LinesDirection of Electric Field Points along Line

Field Lines

Isolated Positive Charge

Isolated Negative Charge

+ _+

+

Begin and End on Charges or Infinity; Never Cross

Draw the Electric Field Lines for 2 negative particles

_ _

The E of a Uniformly Charged Spherical Shell

rr

QEsphere ˆ

4

12

0

for r>R (outside)

0sphereE

for r<R (inside)

Recall this every night before bed!

What does E look like very far away?

Things to do

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• Homework on Quest: Due 9/2• Read Ch14.1-14.8• i-Clickers (register on Quest)