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Dr. W. Oko ń Office: ABB-150 E-mail: okon@physics.mcmaster.ca Office Hours: Mon, Thur 3-4pm PowerPoint Presentation
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Dr. W. Oko ń Office: ABB-150 E-mail: okon@physics.mcmaster.ca Office Hours: Mon, Thur 3-4pm - PowerPoint PPT Presentation


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PHYSICS 2A03. Dr. W. Oko ń Office: ABB-150 E-mail: okon@physics.mcmaster.ca Office Hours: Mon, Thur 3-4pm. Course web page – all lecture notes will be posted here: http://physwww.mcmaster.ca/~okon/2A03/2A03.html. How to do well in this course.

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PHYSICS 2A03

Dr. W. OkońOffice: ABB-150

E-mail: okon@physics.mcmaster.ca

Office Hours: Mon, Thur 3-4pm

Course web page – all lecture notes will be posted here:

http://physwww.mcmaster.ca/~okon/2A03/2A03.html

how to do well in this course
How to do well in this course

Download and print the lecture notes in Power Point format from the web page. Bring the notes to class and add your own notes to them during the lecture. Read the textbook, either before or after the lecture, and add to your notes as you read.Start working on the assignments right away, not the day before they are due!Start studying/reviewing for the test/exam a week before, not the night before!

Ask questions, I ‘may’ have the answers 

physics 2a03
PHYSICS 2A03

I. Electrostatics

II. DC Circuits

III. Magnetism

introduction
Introduction

How do things interact?

  • Gravity

- a force between masses

- holds planets in orbit, etc.

  • Electromagnetism

- a force between charges

- responsible for all familiar forces (except gravity) – friction, normal, magnetic

  • Weak Nuclear Force- decay of particles
  • Strong Nuclear Force

- holds nuclei together

electric charge

+

-

+

-

Electric Charge
  • A scalar quantity
  • Comes in “positive” and “negative”

+

REPEL

-

REPEL

ATTRACT

Units: coulomb, C

and also “smallest unit of charge”, e 1.60210-19 C

electric charge6
Electric Charge
  • Charge often appears in nature in units of “e”:

eg: ParticleCharge

electron -e

proton +e

  • Net charge is a conserved quantity: that is,
  • the algebraic sum of positive and negative charges
  • is constant. Eg +5e-3e = +2e = +8e-6e
slide7
Insulators: charges do NOT move eg: glass, rubber, paper

- can be charged by rubbing, but charges do not move

Conductors: (some) charges move freely eg: metals, some liquids

Semiconductors: electrical properties between insulators and conductors eg: silicon, germanium

slide8

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- -

- -

- -

Quiz

The conductor is neutral (no net charge). When a charged rod is brought close to it (without touching) the net force on the conductor will be:

  • attractive
  • repulsive
  • zero
  • it depends whether the rod is positive or negative

Conductor

Question: did any charges move, if so why?

coulomb s law
Coulomb’s Law

Point charges exert forces on each other:

is a unit vector parallel to r

(Coulomb’s constant)

slide10

Ex1: Find the magnitude of the force between the charges

+10 C and -5 C separated by 20 cm.

slide11

Example:

  • GIVEN:
  • Identical Masses, m=1.0 gram
  • Equal charges q
  • L= 60 cm FIND: q

L

L

m

m

q

q

(equilibrium)

slide12

Quiz:

What happens to each angle if

the charge on the left is doubled, and the other one is halved? Assume mass of charges is small compared to mass of ball.

L

?

L

?

m

m

2q

q/2

(equilibrium)

finding resultant force vector
Finding Resultant force vector:

Find: Force (vector) on q3 , in Cartesian form.

300mm

400mm