1 Announcements: Tutorials Tutorials: Monday 6-8pm Ryan Best Tuesday 4:30-6:30pm Christine Carlisle Wednesday 4:30-6:30pm Christine Carlisle Thursday 6-8pm Ryan Best Tentatively Olin 103 Learning Assistance Center: Has done group tutoring before for Phy 113.

2 Announcements: Labs and Webassign Buy the lab manual Lab’s start next week. Sections A-C are virtually full, section D is nearly empty. Webassign 3 people didn’t do the reading quiz for today. Note, I often comment on reading quizzes. registration requires an access code online or bookstore

Recap When are reading quizzes due? A)MWF 7am B)MWF 10pm C)TR 7am D)F 10pm When are homeworks due? A)MWF 7am B)MWF 10pm C)TR 7am D)F 10pm Suppose a plane flies 100 miles NW. What is the displacement of the plane? A)70.7 x y B)-70.7 x y C)100 x D)100 y

Vector Multiplication There are two ways (in 2 or 3D) to multiply vectors. Scalar product -> two vectors make a scalar A ●B =N Vector product -> two vectors make a vector A x B = C Also called the dot product or the inner product Also called the cross product, alternating product or the outer product

Scalar Product Scalar product -> two vectors make a scalar A ●B =ABcos  A ●B =a x b x +a y b y +a z b z Geometric Algebraic

Vector Product Vector product -> two vectors make a vector Geometric Algebraic C has magnitude absin  Direction perpendicular to the plane containing A and B. A x B = C A x B = (a y b z -b y a z )i+(a z b x -b z a x )j+(a x b y -b x a y )k

The right hand rule velocity v Magnetic Field B Force F F=q(v x B)

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 large unit of charge. 1 electron has -1.6 x C 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  C B)-3  C C)13  C D)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 Conductor A material that allows electrons or other charged particles to flow freely Insulator A material that resists the flow of electrons and other charged particles What do you think of when you hear the words conductor or insulator?

Elementary Charge Charges exist in integer multiples of a fundamental charge unit called e We will consider e to be a positive number (some sources treat it as negative) e =  C the magnitude of the charge on an electron. the charge on a proton When you write that an atom or molecule has a charge +1, you mean +e. A partial charge means that a charge density can be modeled as having a charge at a location less than e

12 Charge Densities Charge can be localized to discrete points (point charges), or it may be spread out over a volume, a surface or a line Charge density  units C/m 3 Surface charge density  units C/m 2 Linear charge density units C/m A cube with side 1 cm has a charge density of  = 1 C/m 3. What is the charge of the cube? A)1 C B)0.01 C = 10 mC C)10 -4 C = 100  C D)10 -6 C = 1  C 1 cm

13 Coulomb’s Law Like charges repel, unlike charges attract Force is directly along a line joining the two charges q1q1 q2q2 r An inverse square law, just like gravity Can be attractive or repulsive – unlike gravity Constant is enormous compared to gravity  0 =  C 2 / (N●m 2 ) Permittivity of free space

14 Coulomb’s Law: Applied A Helium nucleus (charge +2e) is separated from one of its electrons (charge –e) by about 3.00  m. What is the force the nucleus exerts on the electron? Is it attractive or repulsive? r = 3.00  m q 1 =  C q 2 =  C k e =  10 9 N  m 2 /C 2 F e =  N Attractive Force We just calculated the force on the electron from the nucleus. How does this compare with the force on the nucleus from the electron? A)The force on the nucleus is twice as big B)The force on the nucleus is half as big C)The forces are equal in magnitude How does the acceleration of the nucleus compare to that of the electron? A)The acceleration of the nucleus is larger B)The acceleration of the nucleus is smaller C)The accelerations are equal.

15 Newton’s Laws and Kinematics Newton’s laws and all the kinematics you learned in 113 are still true! If a does not depend on time, then