## The Physics

Q: What is the definition of one Coulomb?

A: The official definition is somewhat indirect. But an equivalent definition is that it is the magnitude of the electric charge of a certain number of electrons; i.e. 6.2415096295265x10^(18) electrons.

Q:You said electrons are the smallest particles. Aren't quarks smaller?

A: Actually quarks and electrons are both elementary particles: as far as we know they are not made of anything smaller. A proton is made of three quarks so it is not elementary.

Q: Can't a scalar have a magnitude also, just like a vector?What is the difference between a vector and a scalar then?

A: The magnitude of a vector and a scalar are both positive numbers. Given its magnitude, you just need one more bit of information to determine a scalar quantity, its sign. But in the case of a vector, in addition to the magnitude you have to know the direction, which is a lot more information that just a sign. The magnitudes of a scalar and a vector are both denoted by the same symbol : |x| or |r|.

Q: How do electrical cells (commonly called batteries) work?

A: The details of how they work involve a lot of unpleasant chemistry. The short version is that electrons bind more strongly to some molecules than others. By transferring an electron from a molecule where its is loosely bound to another where it is tightly bound we can extract energy: this is how all chemical reactions work. In a cell, chemicals with a greater affinity to electrons are connected to one pole (the positive) and those with a lesser affinity for electrons is connected to the other (negative).If these two poles are connected by a wire, the electrons can flow from the negative side to the positive, releasing some energy, which can be used for some purpose; e.g., produce light or heat.

Q: A positive charge has electric field coming out of it in all directions. So why doesn't the electrical flux cancel out?

A:Electric flux is a scalar not a vector. The flux through each small part of a surface is the dot product of the electric field at the point with its area; recall that the area is a vector that points normal to the surface. So if you imagine a sphere that surrounds a positive charge, it is true the electrical field can point in different directions at different points; but at any point on the sphere, the electric field and the area vector both point outward, so that the flux is positive. At the opposite point, the electric field has reversed, but so has the area vector. So the total flux is the sum of positive quantities.

## Teaching and Learning

Q: I have a class during your regular office hours. When can I meet with you?

A: Meeting with you is part of the job. Send me email at rajeev@pas.rochester.edu and we will work out a time to meet. Do not wait till the day or week before the exam if you feel confused about something.

Q:Where can I get additional help? I feel lost.

A: The first stop is your workshop leader. Look in the People page for their office hours, which are held in the POA Library. You can talk to any of the TAs at their office hours, not necessarily your own workshop leader. Also, the Society of Physics Students volunteers for FREE tutoring on weekdays (except Fridays) 7:00-9:00 pm and Fridays 2:00-4:00 pm, also at the POA Library. If you feel lost it is important that you come see me during my own office hours, Tue 2:00-3:00; or talk to me after class.

Q: What can I do to improve my performance in the course?

A: There is a great deal you can do on your own to improve your understanding of physics. Each person studies differently, so it is hard to give a general answer. Here are some ideas.

Like any other subject, repetition is a key to understanding physics. Read the lecture notes and the textbook before you come to class. Read them after. Repeat

There are no shortcuts. Physics does not cram well. Start studying it early. Do not fall behind. Study weeks (not days) before an exam. Review after to see where you are doing well and where you need to put in more effort.

Work out the homework problems and additional problems at the back of each chapter of the book. The publisher of the book has a web site, masteringphysics.com which you can use to work out more problems.

Regular workshop attendance correlates well with the grade in the course: generally students say that workshops are more useful than the lecture.

You can read the additional material (other textbooks) on reserve in the library.

The POA library (located on the third floor of the physics building) often has students studying in this and similar courses and you can often get help from them. We have found that the library is a great resource for students this way.

(Did I mention workshops and the POA library?)

## Course Organization

Q: I need to re-schedule workshops (or labs)

Q: Where can I find the homework sets?

A: They are posted on the calendar page, on the square for each Friday. Solutions will be posted on Monday. Lecture notes and suggested reading are posted on Tuesdays and Thursdays.