#### Transcript PHYSICS 1E3 - McMaster Physics and Astronomy

```PHYSICS 1E03
Dr. W. Okoń
Office: ABB-150
e-mail: [email protected]
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
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
A list of suggested problems from the textbook is posted as a
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.
PHYSICS 1E03
I. Electrostatics
II. DC Circuits
III. Magnetism
IV. Waves
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
Electric Charge
• A scalar quantity
• Comes in “positive” and “negative”
+

F
+
-
-
+
-
REPEL

F REPEL
ATTRACT
Units: coulomb, C
and also “smallest unit of charge”, e  1.60210-19 C
Electric Charge (continued)
• 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)
B)
C)
D)
attractive
repulsive
zero
it depends whether the rod
is positive or negative
-----Conductor
Coulomb’s Law
Point charges q1, q2 exert forces on each other:

q1
F
q2
r
F
12
rˆ
21
qq
F k
rˆ
r
1
12
e
2
2
rˆ is a unit vector parallel to r
2
m
ke  8.988x 10 N 
9
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:
GIVEN:
•Identical Masses, m=1.0 gram
•Equal charges q
L
L
•L= 60 cm
30 30
m
q
(equilibrium)
m
q
FIND: Charge, q
Quiz:
L
m
2q
?
? L
(equilibrium)
m
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.
Finding Resultant force vector:
q2  20  C
q4  40C
300mm
400mm
q3  30C
q1  10C
Find: Force (vector) on q3 , in Cartesian form.
solution
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