Transcript week11-faraday

Announcements
Common Exam 3 is on MONDAY Nov 21st
Exam will cover Multi-loop Kirchhoff circuits and RC circuits, Charges and
Currents in Magnetic Fields, and Sources of Magnetic Fields (Biot-Savart,
Amperes Law).
Faraday’s Law of Induction (today’s material)
B will NOT be on Common
Exam III.
A
I will hold an OPTIONAL review for the Common exam on FRIDAY Nov 18th (week
from today) at 10AM. Location Kup 105
C
Announcements
FINAL EXAM is scheduled for TUESDAY
December 20th at 8:30AM
B
…. Last day of final exams
A
C
Clicker Question #0
In the MATRIX trilogy of films, what is the defense of last resort for the humans to
defend their base against invasion from machines?
A) The main character NEO uses his ability to warp the physical laws of the Matrix to
destroy the machines’ source of power.
B) Trinity and Neo team up to destroy Agent Smith who controls the machines.
C) It really does not matter, because we are all in the Matrix right now.
D) Morpheus (Lawrence Fishburn’s character) teaches Neo to navigate the Matrix and
destroy the machines.
A
E) The humans’ spaceship destroys the machines with a pulse of energy.
C
Clicker Question #0
In the MATRIX trilogy of films, what is the defense of last resort for the humans to
defend their base against invasion from machines?
A)
B)
C) It really does not matter, because we are all in the Matrix right now.
D)
E)
We are all just biological batteries…..
A
C
Clicker Question #0
In the MATRIX trilogy of films, what is the defense of last resort for the humans to
defend their base against invasion from machines?
A)
B)
C)
D)
E) The humans’ spaceship destroys the machines with a pulse of energy.
The pulse of energy, called an electromagnetic pulse (sometimes abbreviated EMP) is a
burst of electromagnetic radiation. The abrupt pulse of electromagnetic radiation
usually results from certain types of high energy explosions, (such as a nuclear
explosion), or from a suddenly fluctuating magnetic field. The resulting
rapidly changing
A
electric fields and magnetic fields couple with electrical/electronic systems to produce
damaging current and voltage surges.
Today, we will learn about the basic physics behind this phenomena
C
Faraday’s Law of Induction is all around us….
Experimental Observation
Changing magnetic field through a loop of wire
induces an electromotive force in the wire
which drives a current
Electric Guitars
The magnet in the pickup coil locally magnetizes the guitar string.
“old fashioned” Tape player
In Record mode, Current from coil induces magnetic field in the iron core which
locally magnetizes the tape.
In Playback mode, magnetic areas of the tape induce a changing magnetic flux in
the coil (coupled through the iron) which induces a current to be amplified.
Clicker Question #1
In which direction must the induced EMF and current flow in this loop in order to
oppose the change which made it? HINT: What direction must the current flow to try
to keep the NET B field constant?
A) clockwise
B) counterclockwise
C) No current will flow due to the resistor
B
C
Clicker Question #2
If the B field is decreasing in magnitude, the INDUCED B field and current must be
A) induced B into the page, induced current clockwise
B) Induced B into the page, induced current CCW
C) Induced B out of page, induced current CW
D) Induced B out of page, induced current CCW
B
E) No current is generated since loop is not
Moving.
A
C
External force pulls wire to right. What must the direction of the INDUCED force be to
oppose the motion of the EXTERNAL force?
B
A
C
B
A
C
Clicker Question #3
If the constant external B field OUT OF THE PAGE, the INDUCED B field and current
must be
A) induced B into the page, induced current clockwise
B) Induced B into the page, induced current CCW
C) Induced B out of page, induced current CW
B
D) Induced B out of page, induced current CCW
E) We are in the Matrix…. I can make them move however I want.
A
B
v
C
Transformer can “step up” or “step down” the voltage.
B
A
C
Clicker Question #4
If the constant external B field OUT OF THE PAGE, and a loop of wire is rotating so the
effective area (looking end on) is INCREASING and then DECREASING, the induced
current must
A) Clockwise in both cases
B) CCW in both cases
C) CW then CCW
B
Side view
B
D) CCW then CW
A
E) We are in the Matrix…. The laws of
Physics do not apply.
end view
Leff
B
C
Generation of AC power via the
Faraday effect