Lecture 1-2

Lecture 1-2

Charge - Continued

What’s Happ’nin?

• By now you should have registered on WebAssign and tried the initial assignment.

• You should be reading the first chapter.

• You should have read the syllabus (web).

Summary - Rubbings

- - - + - + - -

Pithy Happenings

Charge Transfer by Contact

Metal Rod Interaction

Induction

More Induction

Magic?

How many ways can we transfer charge? Let us count the ways.

……………..Willie the Shake

• Direct Contact

• Separation of bonds (rubbing, etc,)

• Conduction

• Induction

• Magic.

Coulomb’s Law

• F is a vector.– magnitude– direction

• 1/40=k=8.99 x 109 Nm2/C2

DEFINITION – Unit of Charge is the coulomb

221

04

1

r

QQ

F

Very Important Concepts Very Important Concepts in Physicsin Physics

SSuperposition SSymmetry

Let’s Do Some Problems

• Strategy1. Think about how you will proceed.

2. What information is given, what is missing?

3. Develop the equations in an algebraic format.

4. Solve for an algebraic solution.

5. Plug in the numbers at the end.

6. Look at some special cases to check on consistancy.

7. Think about what you have learned that is worth retaining.

In the figure, a central particle of charge -2q is surrounded by a square array of charged particles, separated by either distance d or d/2 along the perimeter of the square.

In the figure, particle 1 of charge +1.0 µC and particle 2 of charge -4.0 µC, are held at separation L = 11.0 cm on an x

axis. If particle 3 of unknown charge q3 is to be located such that the net electrostatic force on it from particles 1 and 2 is zero, what must be the coordinates of particle 3?

x=[-11] cm y=[0] cm

A mechanics problem from the past!

Free Body Forces?

Find force on lower left particle.Find force on lower left particle.

What is e??

|e|=1.6 x 10-19 Coulombs

Exact value in textbook