October 5, 2011

 Monday ◦ Finish Capacitor Activity ◦ Dielectric in Capacitors ◦ Magnetism, Intro.  Wednesday ◦ Magnetism  Friday ◦ Quiz ◦ Magnetism  Monday ◦ More Magnetism  Wednesday ◦ EXAMINATION #2  Potential  Magnetism – as far as we get  Some old stuff might be necessary. ◦ After Exam – continue with new material DONE

If you want some insight into how this comes about, check the website.

Try not to hurt yourself when these vectors are in difficult orientations!

A vector of magnitude 5 lies along the x axis, and a vector of magnitude 10 lies in the xy plane, 30 degrees from the x axis (see the figure). What is the magnitude and direction of the cross product C x D?

 Made of mysterious materials (lodestone???)  Each Magnet has a North and South pole.  Break a magnet between the N and S pole and you wind up with two magnets, each with a N and S pole.  Magnets produce magnetic fields. (More on that later)  Moving charges also create magnetic fields. This is the next topic that we will discuss and explore now that you have done the experiment on this.

Unit Vector Source Charge Inverse Square Law Vector

Magnetic Permeability of Space Magnetic Field Intensity Tesla Source Current Element Inverse Square q

unit vector

 DISCUSSION ◦ Does this agree with your last experiment? Which kind of current??? ◦ Does this agree with B-S?

WWater current flows down hill. GGravitational Field is pulling it down. TThe flow is from high to low gravitational potential. IIt is hard to swim against the current. EElectric Current flows in a similar way – from high to low electric potential (Voltage).

This is NOT the norm

 The amount of CHARGE that crosses a cross-section of a wire such as this in ONE SECOND is defined as a current of one Ampere.

 The electron current flows against the Electric Field.  The electric field exists because a battery (or something else) creates the electric field.  The conventional current flow is in the direction of the electric field. +  Only the negative electrons actually move. The positive (+) charges remain stationary.

 The electrons “drift” at a drift velocity v.  In time  t they drift a distance v  t.  The volume of electrons that flow in that time is Av  t.  Let n be the number of electrons that can move per unit volume. A

A

Electron Current Conventional Current Electron Current = Number of electrons crossing the area/second Conventional Current = Positive charge crossing area/second

Break a long wire carrying a current I into a bunch of small segments. Express the magnetic field  B at point A in terms of the current element  l. Replace the equation above with this expression.