w13d3 more patterns
DESCRIPTION
Easy!. W13D3 More Patterns. Fields, Patterns, Maxwell’s Equations and Begin Induction/Faraday’s Law 2049 SCALE-UP. Calender. THE EVAN SHOW. Field Patterns From Last Time. “Curly Field” No diverging source. Diverging Field Point Sources. - PowerPoint PPT PresentationTRANSCRIPT
W13D3 More PatternsFields, Patterns, Maxwell’s Equations and Begin Induction/Faraday’s Law2049SCALE-UP
EASY!
CalenderMonday Wednesday Friday Saturday
14
Chapter 22Gauss
16 (Read rest of chapter)2 WebAssignsChapter 22Gauss
18QUIZ
Chapter 22Lentz & More
21
Chapter 23Faraday
23QUIZ
Chapter 23Faraday
HOLIDAY
28
Chapter 23Faraday
30
Chapter 24EM
2Chapter 24 EMOptional Exam
(22-24)
3
FINAL EXAM
THE EVAN SHOW
Field Patterns From Last Time
“Curly Field”No diverging source
Diverging FieldPoint Sources
Electrostatic Fields Magnetic Fields
Maxwell’s Equations
0
0 .
0
? =Faraday's Law of Induction - Next Topic
(One additional term)
inside
inside path
qdA
dA
d
d I
E n
B •n
E l
B l
A puzzlement ..
enclosedid 0 sB
Let’s apply this to the gap of a capacitor.
Consider the poor little capacitor…
i i
CHARGING OR DISCHARGING …. HOW CAN CURRENTFLOW THROUGH THE GAP
In a FIELD description??
Through Which Surface Do we measure the current for Ampere’s Law?
I=0
In the gap… DISPLACEMENT CURRENT
dtd
dtdqI
ntDisplaceme
Idtdq
Letdtdq
dtd
qEA
Ed
d
E
E
0
0
0
2
Current
gap)(in
1
S through FLUX ELECTRIC The
0
0 . 0
0
? =Faraday's Law of Induction - Next Topic
( + )
inside
Einside path
qdA
dA
d
dd I
dt
E n
B •n
E l
B l
NEXT
Fix the Last Maxwell Equation
? =Faraday's Law of Induction - d E l
The Coil and the Magnet
Coil
Galvanometer
Magnetic Flux M
Integral over a SURFACE
What’s Happening Here??
A
Observation
Meter Deflects
There must be an emf around the loops!
VariablesDirectionPolarityPitchVelocity
Down the Hatch
Aluminum Pipe
Down the Hatch
B
Aluminum Pipe
N
S
Induced Current
NREPEL!!
There must bean Electric Fieldin the metal thatis pushing the current!!
You said that there is a conducting loop.You said that there is therefore a current induced around the loop if the flux through the loop changes.But the beginning and end point of the loop are the same so how can there be a voltage difference around the loop?Or a current???‘tis a puzzlement!
HEY BINDELL – WAIT A SECOND …….
REMEMBER when I said E Fields start and end on CHARGES???
DID I LIE??
Electric fields that are created by static charges must start on a (+) charge and end on a (–) charge as I said previously.Electric Fields created by changing magnetic fields (NON-Coulombic) can actually be shaped in loops.
The truth
BUT WAIT, YOU STILL LIE!
Why do you STILL think I am a liar?
Because you said that an emf is a voltage so if I put a voltmeter from one point on the loop around to the same point, I will get ZERO
volts, won’t I? How can there be a current??
Yes … butthis doesn’t make
me a liar!Let Me Explain.
Is the WORK that an external agent has to do to move a unit charge from one point to another.But we also have (neglecting the sign):
The POTENTIAL between two points
sEV
s
So, consider the following:
E
Conductor
x x x x x x xx x x x x x xx x x x x x xx x x x x x xx x x x x x xx x x x x x x
zeroREemf
sEsEemf
2
THEREFORE WHAT WILL A VOLTMETER READ FROM A to A?
E
Conductor
x x x x x x xx x x x x x xx x x x x x xx x x x x x xx x x x x x xx x x x x x x
A
A The emfB ZeroC Can’t tell
How Big is the emf?
temf loopthe
Through
Faraday’s Law
Michael Faraday (1791-1867)
MINUS????
Q: Which way does E point?A: The way that you don’t want it to point! (Lenz’s Law).
Lenz’s Law Explains the (-) sign!
Push a magnet into a coil of two wires and a current is produced via an emf.
In this case, 2 coils, each have the SAME emf so we add..Ohm’s Law still works, so
coilRemfi
tNemf
Faraday’s Experiments
??
Insert Magnet into Coil
Remove Coil from Field Region
That’s Strange …..
These two coils are perpendicular to each other
All Involve Changing The Magnetic
Flux through the Loops
Remember the Definition of TOTAL ELECTRIC FLUX through a CLOSED surface:
dA
is surface aLEAVING FieldElectric theofFlux Total
outE
surface EE d
nE
Magnetic FluxApplies to an OPEN SURFACE only.“Quantity” of magnetism that goes through a
surface.
AB dBsurface
In the figure below a 120-turn coil of radius 1.8 cm and resistance 6.8 W is coaxial with a solenoid with 209 turns/cm and diameter 3.2 cm. The solenoid current drops from 1.5 A to zero in time interval Δt = 25 ms. What current is induced in the coil during Δt?
0.0224 A
DONE