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October 5, 2011 Monday ◦ Finish Capacitor Activity ◦ Dielectric in Capacitors ◦ Magnetism,...
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W7D2 Magnetism October 5, 2011
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Transcript of October 5, 2011 Monday ◦ Finish Capacitor Activity ◦ Dielectric in Capacitors ◦ Magnetism,...
W7D2 MagnetismOctober 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
This week
DONE
From the textbook…..
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!
The Right Hand Rule
Can you do this?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.
Magnets
Remember Coulomb?
Unit Vector
Source Charge
Inverse Square Law
Vector
Biot-Savart Law
02
270
4
Tesla-m1 10 (Exactly)
4 /
unitqv rB
r
Coulomb m s
Magnetic Permeability of
Space
Magnetic Field
IntensityTesla
SourceCurrentElement
Inverse Squareq
unit vector
B is a VECTOR (Unit – Weber)
B Activity
DISCUSSION◦ Does this agree
with your last experiment? Which kind of current???
◦ Does this agree with B-S?
Magnetic Field Around a Wire
Water current flows down hill.
Gravitational Field is pulling it down.
The flow is from high to low gravitational potential.
It is hard to swim against the current.
Electric Current flows in a similar way – from high to low electric potential (Voltage).
Let’s Discuss Current
02
270
4
Tesla-m1 10 (Exactly)
4 /
unitqv rB
r
Coulomb m s
CCCCCCCCCCCCCC
This is NOT the
norm
One Charge q is NOT thenorm .. A CURRENT is!
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.
Electric Current-1
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.
Electric Current-2
The electrons “drift” at a drift velocity v. In time Dt they drift a distance vDt. The volume of electrons that flow in that time is AvDt. Let n be the number of electrons that can move per
unit volume.
Electric Current-3
A
Electric Current-4
A
(number of charges in the volume) x (charge/carrier)current=
(Amps)
timenA v e t
i nA v et
IMPORTANT !
Electric Current
Electron Current
ConventionalCurrent
Electron Current = Number of electrons crossing the area/second
Conventional Current = Positive charge crossing area/second
Which current is this equation for?
(number of charges in the volume) x (charge/carrier)current=
(Amps)
timenA v e t
i nA v et
IMPORTANT !
NO BOOKS – Just material from this lecture!!
Break a long wire carrying a current Iinto a bunch of small segments. Expressthe magnetic field DB at point A in terms of the current element Dl. Replace the equation above with this expression.
