Dr. W. Oko ń
Office: ABB-150 e-mail: okon@physics.mcmaster.ca
Class: Tue/Thu 9-12
Office Hours: Tue/Thu 12:15-1:15pm
Course web page – I will be posting news and all lecture notes here: http://physwww.mcmaster.ca/~okon/1e03/1e03s.html
Textbook: Serway (any edition is OK)

Components of the course
- Labs: 15%
- Participation (i-clicker) 5%
- One term tests, 90min. Total 30% (MC + long)
- Final exam, 3 hours. 50% (MC + long)
Test Rooms – TBA
Labs – start next Tues. We will automatically replace your lab mark with your old mark if you have done ALL of the labs previously

Homework + Doing Well
Download and print the lecture notes in Power Point format from the my web page. Bring the notes for class and add your own notes to them during the lecture. Read the textbook, either just before or just after the lecture, and add to your notes as you read. Try to solve all the assignment problems, these are very helpful for the tests!
A list of suggested problems from the textbook is posted as a file. You can download and print these. As we cover the material from the textbook you can try to do the appropriate questions from this list if you’re done all the assignments.
Do NOT work alone, find someone to solve the problems with and talk about them/physics. For the multiple choice type questions, look at the Quick Quizzes in the textbook, and old tests online.

Introduction
How do things interact?
1) Gravity
- a force between masses
- holds planets in orbit, etc.
2) Electromagnetism
- a force between charges
- responsible for all familiar forces (except gravity) – friction, normal, magnetic
3) Weak Nuclear Force
- decay of particles
4) Strong Nuclear Force
- holds nuclei together

F

• A scalar quantity
• Comes in “positive” and “negative”
+
-
+
+
-
-
REPEL
F

REPEL
ATTRACT
Units: coulomb, C and also “smallest unit of charge”, e   1.602
 10 -19 C

• Charge appears in nature in units of “e”: eg: Particle electron proton
Charge
-e
+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

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

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:
A) attractive
B) repulsive
C) zero
D) it depends whether the rod is positive or negative
Conductor

Point charges q , q
2 q
1 exert forces on each other: q
2 r

F
12
F
21
rˆ
F
12
 k e q q
1 2 r 2 r is a unit vector parallel to r r
k e

8
.
988 x
10
9 N  m 2
C 2
(Coulomb’s constant)

Example 1 : Find the magnitude of the force between the charges +10  C and -5  C separated by 20 cm.

Example 2:
L L m q
30

30

(equilibrium) q m
GIVEN:
•Identical Masses, m=1.0 gram
•Equal charges q
•L= 60 cm FIND: Charge, q

Quiz: m
2q
L
? ?
L m
(equilibrium) q/2
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.

q
2
 
20

C
300mm q
3

30
 C
400mm q
4

40

C q
1
 
10
 C
Find: Force (vector) on q
3
, in Cartesian form.

solution