Physics 114

Professor Fred Salsbury Office Hours: MWF 11-11:40am; M 1-2pm 301A Olin http://www.wfu.edu/~salsbufr

http://www.webassign.netsalsbufr@wfu.edu

Topics Covered•Electricity and Magnetism•E&M Waves•Nuclear Physics

Please Pick Up and READ the Course Policy &Syllabus

Class Participation

•Cut out your voting cards and bring them to every class •If you forget them, borrow some from me•If you lose them, get new ones from me•We will be using them for Concept quizzes in-class

Reading Assignments and QuizzesReading AssignmentsRequired:

Every Lecture starting Wed; quizzes coverRecommended:

ApplicationsOnline exercises

Extra:More rigorous mathematical treatments

Recommended and Extra will be on reserve at the libraryAlong with two mathematics review texts.Reading quizzes,

due 7am before every lecture; starting WedA few submissions per problemsWork by yourself

Homework and Semester Quizzes

Homework AssignmentsRequired:

Every Lecture Starting FridaySeveral SubmissionsEncouraged to work with others, butyou must submit your own work.

Semester quizzesFour – see syllabus for datyesLowest score is weighted ½

Grading

Final Exam 330 points Semester Quizzes 350 points Laboratory ,Homework and Reading Quizzes 320 points

Total 1000 points

If you miss any semester quiz or exam, I need a note from a medical doctor or the Dean’s office.

You must pass lab to pass the course.You are expected to pass the final.

Webassign•http://www.webassign.net/student.html

•Username is your email (without @wfu.edu)•Institution is wfu•Password (if new to webassign) is your student number•If you have used webassign before use your old password.

Log into webassign ASAP.If you have difficulty, contact me.

There is a test homeworkon using webassign.

Web InformationHow to access course info:•Go to www.wfu.edu/~salsbufr•Click on teaching•There will be a page for general announcements, and a sidebar filled with useful information; including lecture notes.

•This course does not use blackboard.

Survey

•Online at webassign•Worth 2 points if completed•Due Wednesday•To provide me with a idea of your backgrounds and expectations, and tutorial times.

Coordinate systemsDifferent ways of representing space, and physics.Some problems are easier in some coordinate systems, but the physics is invariant.

Cartesian Coordinates:

sin

cos

ry

rx

x

ytan 22 yxr

Polar CoordinatesAnother popular coordinate system, along with cylindricaland spherical

Vectors: Magnitude and direction

Scalars: Magnitude

Vectors and Scalars

Displacement is a vector.Velocity is a vector.Acceleration is a vector.

sin

cos

AA

AA

y

x

The x- and y-components of a vector:

22yx AAA

The magnitude of a vector:

x

y

A

A1tanThe angle between vector and x-axis:

Vector Components: Geometric

A = Axi + Ayj

Vector Components: Algebraic• A unit vector is a dimensionless vector having a magnitude 1.

• Unit vectors are used to indicate a direction.

• i, j, k represent unit vectors along the x-, y- and z- direction .

• is another common notation.

• i, j, k form a right-handed coordinate system.

z,y,x

We want to calculate: R = A + B

From diagram: R = (Axi + Ayj) + (Bxi + Byj)

R = (Ax + Bx)i + (Ay + By)j

Vector Addition: Algebraic I

Rx = Ax + Bx

Ry = Ay + By

The components of R:

2222 )()( yyxxyx BABARRR

The magnitude of R:

xx

yy

x

y

BA

BA

R

RtanThe angle between vector R and x-axis:

Vector Addition: Algebraic II

Vector MultiplicationThere are two ways (in 2 or 3D) to multiply vectors.

Scalar product -> two vectors make a scalar

NBA

Vector product -> two vectors make a vector

CBA

Also called the dot productor the inner product

Also called the cross productor the outer product

Scalar ProductScalar product -> two vectors make a scalar

cosabBA

zzyyxx bababaBA

Geometric

Algebraic

Vector ProductVector product -> two vectors make a vector

CBA

kabbajabbaiabbaBA yxyxxzxzzyzy )()()(

Geometric

Algebraic

C has magnitude absinDirection perpendicularto the plane containing A and B.

The right hand rule

velocity vMagnetic Field B

Force F

F q v B

sinF qvB

Electricity and Magnetism

•One of the four fundamental forces of nature •Responsible for the vast majority of what we observe around us•Probably best-understood and best-tested of the forces of nature

Electromagnetic Interactions:•Electricity and Electronics•Magnetism•Chemistry•Biology• and even more

Electrical Charges•Electric forces only affect objects with charge•Charge is measured in Coulombs (C). A Coulomb is a lot of charge!•Charge comes in both positive and negative quantities•Charge is conserved – it can neither be created nor destroyed•Charge is usually denoted by the letter q.

An object has a total charge of 5 C. It is divided into two pieces, one of which has charge 8 C and the other of which has charge

A) 3 CB) -3 CC) 13 CD) Such a division is impossible

Matter and Charges•All matter is made of positive and negative charges (or neutral)•An object’s total charge is very close to zero•When an object becomes charged, a tiny fraction of its charged

particles (usually electrons) are lost or gained•These particles (usually electrons) can flow through objects•Some materials are better at allowing the flow of electrons than others

ConductorA material that allows

electrons or other charged particles to

flow freely

InsulatorA material that resists the flow of electrons

and other charged particles

Elementary Charge•Charges seem to come only in integer multiples of a fundamental charge unit called e •We will treat e as a positive number (some sources treat it as negative)

e = 1.602 10-19 C

know these

Particle qProton eNeutron 0Electron -eOxygen nuc. 8eCalcium ion 2eChlorine ion -e