## Rabu, 01 September 2010

### Fisika untuk Universitas

Fisika untuk Universitas

Ditujukan untuk meningkatkan kualitas proses dan hasil perkuliahan Fisika di tingkat Universitas

Kelistrikan dan Kemagnetan

Topics covered:

Electric Flux
Gauss's Law
Examples

Instructor/speaker: Prof. Walter Lewin

### Video

Today we're going to work on a whole new concept and that is the concept of electric flux.

We've come a long way.

We started out with Coulomb's law.

We got electric field lines.

And now we have electric flux.

Suppose I have an electric field which is like so and I bring in that electric field a surface, an open surface like a handkerchief or a piece of paper.

And so here it is.

Something like that.

And I carve this surface up in very small surface elements, each with size dA, that's the area, teeny weeny little area, and let this be the normal, N roof, the normal on that surface.

So now the local electric field say at that location would be for instance this.

It's a vector.

The electric flux d-phi that goes through this little surface now is defined as the dot product of E and the vector perpendicular to this element which has this as a magnitude dA.

Now our book will always write for ndA simply dA.

So I will do that also although I don't like it but I will follow the notation of the book.

So this vector dA is always perpendicular to that little element dA and it has the magnitude dA.

And so this since it is a dot product is the magnitude of E times the area dA times the cosine of the angle between these two vectors, theta.

And this is scalar.

The number can be larger than zero, smaller than zero, and it can be zero.

And I can calculate the flux through the entire surface by doing an integral over that whole surface.

The unit of flux follows immediately from the definition.

That is Newtons per Coulombs for the units of this flux, is Newtons per Coulombs times square meters.

But no one ever thinks of it that way.

Just SU SI units.

I can give you-- a some intuition for this flux by comparing it first with an airflow.

These red arrows that you see there represent the velocity of air and you see there a black rectangle three times.

In the first case notice that the normal to the surface of that area is parallel to the velocity vector of the air and so if you want to know now what the amount of air is in terms of cubic meters per second going through this rectangle it would be V times A.

It's very simple.

Pengembangan Perkuliahan

1. Buatlah sebuah Esai mengenai materi perkuliahan ini

2. Buatlah sebuah kelompok berjumlah 5 orang untuk menganalisis materi perkuliahan ini

3. Lakukan Penelitian Sederhana dengan kelompok tersebut

4. Hasilkan sebuah produk yang dapat digunakan oleh masyarakat

5. Kembangkan produk tersebut dengan senantiasa meningkatkan kualitasnya

Ucapan Terima Kasih Kepada:

1. Para Dosen MIT di Departemen Fisika

a. Prof. Walter Lewin, Ph.D.

b. Prof. Bernd Surrow, Ph.D.

#### Staff

Visualizations:
Prof. John Belcher

Instructors:
Dr. Peter Dourmashkin
Prof. Bruce Knuteson
Prof. Gunther Roland
Prof. Bolek Wyslouch
Dr. Brian Wecht
Prof. Eric Katsavounidis
Prof. Robert Simcoe
Prof. Joseph Formaggio

Dr. Peter Dourmashkin
Prof. Robert Redwine

Technical Instructors:
Andy Neely
Matthew Strafuss

Course Material:
Dr. Peter Dourmashkin
Prof. Eric Hudson
Dr. Sen-Ben Liao

#### Acknowledgements

The TEAL project is supported by The Alex and Brit d'Arbeloff Fund for Excellence in MIT Education, MIT iCampus, the Davis Educational Foundation, the National Science Foundation, the Class of 1960 Endowment for Innovation in Education, the Class of 1951 Fund for Excellence in Education, the Class of 1955 Fund for Excellence in Teaching, and the Helena Foundation. Many people have contributed to the development of the course materials. (PDF)

2. Para Dosen Pendidikan Fisika, FPMIPA, Universitas Pendidikan Indonesia.

Terima Kasih Semoga Bermanfaat dan mohon Maaf apabila ada kesalahan.