Selasa, 10 Agustus 2010

Fisika untuk Universitas

Fisika untuk Universitas

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

Kelistrikan dan Kemagnetan

Topics covered:

What holds our world together?
Electric Charges (Historical)
Electric Force
Coulomb's Law

Instructor/speaker: Prof. Walter Lewin

Free Downloads



Course Meeting Times

Lectures: 3 sessions / week, 1 hour / session
Recitations: 2 sessions / week, 1 hour / session

Course Description






Lectures - Homework - Solutions - Exams - Quizzes - Grades




There will be no make-up exams!




» Download this transcript (PDF)

I'm Walter Lewin.


The book will support my lectures.

My lectures will support the book.

You will not see any tedious derivations in my lectures.

For that we have the book.



And you may even start to like it.

I suggest you do not slip up, not even one day, eight o two is not easy.


Electricity and magnetism is all around us.

We have electric lights, Electric clocks.


Light itself is an electromagnetic phenomenon as radio waves are.


And I will teach you about that in this course.

Cars, planes, trains can only run because of electricity.

Horses need electricity because muscle contractions require electricity.

Your nerve system is driven by electricity.

Atoms, molecule, all chemical reactions exist because of electricity.

You could not see without electricity.

Your heart would not beat without electricity.

And you could not even think without electricity, though I realize that even with electricity some of you may have a problem with that.

The modern picture of an atom is a nucleus, which is very small compared to the size of the atom.

The nucleus has protons, which are positively charged and it has neutrons, which have no charge.

The mass of the proton is approximately the same as the mass of the neutron.

It's about six point seven times ten to the minus twenty-seventh kilograms.

One point seven.

The positive charges here with the nucleons, with the neutrons, and then we have electrons in a cloud around it.

And if the atom is neutral, the number of electrons and the number of protons is the same.

If you take one electron off you get a positive ion.

If you add an electron then you get a negative ion.

The charge of the electron is the same as the charge of the proton.

That's why the number is the same for neutral atoms.

The mass of the electron is about eighteen hundred thirty times smaller than the mass of the proton.

It's therefore negligibly small in most cases.

All the mass of an atom is in the nucleus.

If I take six billion atoms lined up touching other, I take six billion because that's about about the number of people on earth.

Then you would only have a length of sixty centimeters.

Gives you an idea of how small the atoms are.

The nucleus has a size of about ten to the minus twelve centimeters.

And the atom itself is about ten thousand times larger.

The cloud of electrons, which is about ten to the minus eight centimeters.

And if you line six billion of those up you only get this much.

Already in six hundred BC, it was known that if you rub amber that it can attract pieces of dry leaves.

And the Greek word for amber is electron.

So that's where electricity got its name from.

In the sev- sixteenth century there were more substances known to do this.

For instance glass and sulfur.

And it was also known and written that when people were bored at parties that the women would rub their amber jewelry and would touch frogs, which then would start jumping of desperation, which people considered to be fun, not understanding what actually was happening to the amber nor what was happening to the frogs.

In the eighteenth century it was discovered that there are two types of electricity.

One if you rub glass and another if you rub rubber or amber for that matter.

Let's call one A and the other B.

It was known that A repels A and B repels B but A attracts B.

And it was Benjamin Franklin without any knowledge of electrons and protons who introduced the idea that all substances are penetrated with what he called electric fluid, electric fire.

And he stated if you get too much of the fire then you're positively charged and if you have a deficiency of that fire, then you're negatively charged.

He introduced the sign convention and he decided that if you rub glass that that is an excess of fire and he called that therefore positive.

You will see later in this course why this choice he had fifty percent chance is extremely unfortunate but we have to live with it.

So if you take this fluid according to Benjamin Franklin and bring it from one substance to the other, then the one that gets an excess becomes positively charged but automatically as a consequence of that the one from which you take the fluid becomes negatively charged.

And so that's the whole idea behind the conservation of charge.

You cannot create charge.

If you create plus then you automatically create minus.

Plus and plus repel each other.

Minus and minus repel each other.

And plus and minus attract.

And Benjamin Franklin who did experiments also noticed that the more fire you have the stronger the forces.

The closer these objects are to each other, the stronger the forces.

And there are some substances that he noticed, which conduct this fluid, which conduct this fire, and they are called conductors.

If I have a glass rod as I have here and I rub it then it gets this positive charge that we just discussed.

So here is this rod and I rub it with some silk and it will get positively charged.

What happens now to an object that I bring close to this rod and I will start off with taking a conductor.

And the reason why I choose a conductor is that conductors have a small fraction of their electrons, which are not bound to atoms but which can freely move around in the conductor.

That's characteristic for a conductor, for metals.

That's not the case with nonconductors.

There the all electrons are fixed to individual atoms.

So here we have a certain fraction of electrons that can wander around.

What's going to happen that electrons want to be attracted by these positive charges.

Plus and minus attract each other.

And so some of these electrons, which can freely move will move in this direction and so the plus stay behind.

This process we call induction.

You get sort of a polarization.

You get a charge division.

It's a very small effect, perhaps only one in ten to the thirteen electrons that was originally here will end up here but that's all it takes.

So we get a polarization and we get a little bit more negative charge on the right side than we have on the left side.

And so what's going to happen is, since the attraction between these two will be stronger than the repelling force between these two because the distance is smaller and Franklin had already noticed the shorter the distance the stronger the force.

What will happen is that if this object is free to move it will move towards this rod.

And this is the first thing that I would like you to see.

I have here a conductor that is a balloon, helium-filled balloon.

And I will rub this rod with silk.

And as I approach that balloon you will see that the balloon comes to the rod.

I will then try to rub with that rod several times on that balloon.

It will take a while perhaps because the rod itself is a very good nonconductor.

It's not so easy to get charge exchange between the two.

But if I do it long enough I can certainly make that balloon positive.

Then they're both positive.

And then they will repel each other.

But first, the induction part, whereby you will see the balloon come to the glass rod.

These experiments work best when it is dry, in the winter.

They don't work so well when it is humid so it's a good time to teach eight o two in the winter.

OK there we go this should be positively charged now.

And the balloon wants to come to the glass.

You see that?

Very clearly.

Pengembangan Perkuliahan

1. Buatlah sebuah Esai mengenai 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.


Prof. John Belcher

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

Course Co-Administrators:
Dr. Peter Dourmashkin
Prof. Robert Redwine

Technical Instructors:
Andy Neely
Matthew Strafuss

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




Terima Kasih Semoga Bermanfaat dan mohon Maaf apabila ada kesalahan.

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