1. Dr. W. Okoń 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 PHYSICS 2A03

2. 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

3. PHYSICS 2A03 I.Electrostatics II. DC Circuits III. Magnetism

4. Introduction 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 How do things interact?

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

6. Electric Charge Net charge is a conserved quantity: that is, the algebraic sum of positive and negative charges is constant. Eg +5e-3e = +2e = +8e-6e Charge often appears in nature in units of “e”: eg:ParticleCharge electron -e proton +e

7. 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

8. - Conductor 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 Question: did any charges move, if so why?

9. Coulomb’s Law Point charges exert forces on each other: (Coulomb’s constant) is a unit vector parallel to r

10. Ex1: Find the magnitude of the force between the charges +10  C and -5  C separated by 20 cm.

11. Example: L L mm qq GIVEN: Identical Masses, m=1.0 gram Equal charges q L= 60 cm FIND: q (equilibrium)

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

13. Finding Resultant force vector: Find: Force (vector) on q 3, in Cartesian form. 400mm 300mm

14. Solution