Standards/Plan

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Standards/Plan
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Standards
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Standards
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Standards
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Standards
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WARM UP
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Simple Harmonic Motion (SHM)

• 1) An electron is fired up between two charged
  plates, as shown. Which of the following
  identifies the field and motion of the electron
  as it passes through the field?

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Simple Harmonic Motion (SHM)

• 2) An insulating plate is rubbed with a cloth to
  give it a charge. A conducting plate, attached to
  an insulating handle, is then placed on top of
  the insulator and briefly grounded by touching
  it. The conductor is held by the insulating
  handle and lifted from the insulator plate. Which
  of the following is true?

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Simple Harmonic Motion (SHM)
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Warm Up

• 3) If the voltage across a circuit is kept
  constant and the resistance is halved, by what
  factor does the circuits current change?
• a) 1/2 c) 1/4
• b) 2 d) 4
• 4) If the current supplied to a resistor is
  tripled,, by what factor does the circuits power
  change?
• a) 1/3 c) 1/9
• b) 3 d) 9

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Warm Up

• 5) A computer monitor runs on 120 Volts, and has
  a resistance of 100 ohms. The amount of power it
  dissipates is closest to

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Warm Up

• 5)

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Warm Up

• 6) What is the equivalent resistance of the
  circuit?

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Warm Up

• 7) A battery (of voltage V or 2V) and resistors
  (of R or 2R) are connected in various
  combinations as shown below. In which circuit is
  the most power dissipated?

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Warm Up

• 8) Which 2 circuits have the same total current
  in the circuit?

1. A and C
2. A and E
3. B and C
4. A and B
5. B and D

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Warm Up
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Warm Up

• 9) A resistor, R1 is connected to a battery and
  is dissipating energy at a rate of P. A second
  resistor, R2 connected to a battery of the same
  voltage dissipates energy at a rare of 2P. What
  is the resistance of R2?

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Warm Up

• 9) ANSWER D
• A resistor, R1 is connected to a battery and is
  dissipating energy at a rate of P. A second
  resistor, R2 connected to a battery of the same
  voltage dissipates energy at a rare of 2P. What
  is the resistance of R2?

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Warm Up

• 10) The following magnetic field is directed
• 11) The magnetic force on the particle is
  directed
• Top of page
• Right
• Into the page
• Out of the page
• Bottom of page

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Announcements

• Submit quiz corrections
• MAKE UP WORK
• I will be after school TODAY!
• Quizzes and Tests!

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Magnetic Fields

• Magnets produce MAGNETIC FIELDS
• Lines start from the NORTH pole and LOOP toward
  the SOUTH pole.
• Opposite poles ATTRACT
• Like poles REPEL

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Compasses

• Compasses will ALIGN themselves to a magnetic
  field.

Magnetic Monopoles

• Do not exist

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Field Geometry

• A magnetic field can point
• Left Right
• Top of page Bottom of page
• Into the page Out of the page

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Field Geometry

• A magnetic field can point

• How to remember into the page and out of the
  page
• Point of arrow coming at you INTO the
  page
• Tail of arrow moving away from you OUT OF
  PAGR

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Magnetic Force on Particles

• A magnetic force is exerted on a particle within
  a magnetic field only if
• Particle has a CHARGE
• Velocity is PERPENDICULAR

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Magnetic Force Equation

• F qvBsin?
• q charge in Coulombs
• v speed in meters/second
• B magnetic field in Tesla
• ? angle between v and B

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Example Problem

• F qvBsin?
• Calculate the magnitude force exerted on a 3.0 C
  charge moving north at 1,000 m/s in a magnetic
  field of 0.2T if the field is directed to the
  east.

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• F qvBsin?
• A B field is directed SOUTH
• Is there a force if the particle moves.
• North ?
• South ?
• East ?
• West ?
• Up ?
• Down ?

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Vector Direction ?The Right Hand Rule

1. Velocity Thumb
2. B Field Fingers
3. Palm Force

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• Which way is the force?

Velocity
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• Which way is the force?

Velocity
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• Which way is the force?

Velocity
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• Which way is the force?

Velocity
B
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• Which way is the force?

Velocity
B
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• Which way is the force?

Velocity
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• Which way is the force?

Velocity
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Sample Problem

• Calculate the magnitude and direction of the
  magnetic force.

v 300,000 m/s
34o
q 3.0mC
B 200 mT
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Sample Problem

• Calculate the magnitude and direction of the
  magnetic force.

v 300,000 m/s
34o
q 3.0mC
B 200 mT
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Castle Learning

• 09-14

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Page 2

• Motion of Charged Particles in Magnetic Field

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Magnetic forces

• Must beperpendicular to the velocity AND the
  field (orthoganal)
• Can.
• Accelerate charged particles by changing
  direction.
• cause charged particles to move in circular or
  helical paths.

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Magnetic forces cannot...

• CANNOT.
• Change the speed or kinetic energy of charged
  particles.
• do work on charged particles.

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Magnetic Forces

• are centripetal.
• centripetal acceleration
• v2/r
• centripetal force is therefore
• mv2/r

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Magnetic Forces are Centripetal

• SF ma
• FB Fc
• qvBsin? mv2/r
• qB mv/r
• q/m v/(rB)

B
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Sample Problem

• What is the orbital radius of a proton moving at
  20,000 m/s perpendicular to a 40 T magnetic field?

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Sample Problem

• What is the orbital radius of a proton moving at
  20,000 m/s perpendicular to a 40 T magnetic field?

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Sample Problem

• What must be the speed of an electron if it is to
  have the same orbital radius as the proton in the
  magnetic field described in the previous problem?

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Sample Problem

• What must be the speed of an electron if it is to
  have the same orbital radius as the proton in the
  magnetic field described in the previous problem?

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Sample Problem

• An electric field of 2000 N/C is directed to the
  south. A proton is traveling at 300,000 m/s to
  the west. What is the magnitude and direction of
  the force on the proton? Describe the path of the
  proton? Ignore gravitational effects.

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Sample Problem

• An electric field of 2000 N/C is directed to the
  south. A proton is traveling at 300,000 m/s to
  the west. What is the magnitude and direction of
  the force on the proton? Describe the path of the
  proton? Ignore gravitational effects.

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Sample Problem

• A magnetic field of 2000 mT is directed to the
  south. A proton is traveling at 300,000 m/s to
  the west. What is the magnitude and direction of
  the force on the proton? Describe the path of the
  proton? Ignore gravitational effects.

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Sample Problem

• A magnetic field of 2000 mT is directed to the
  south. A proton is traveling at 300,000 m/s to
  the west. What is the magnitude and direction of
  the force on the proton? Describe the path of the
  proton? Ignore gravitational effects.

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Sample Problem - Electrons switch direction

• Calculate the force and describe the path of this
  electron.

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Sample Problem - Electrons switch direction

• Calculate the force and describe the path of this
  electron.

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Sample Problem - Electrons switch direction

• Calculate the force and describe the path of this
  electron.

B 2000 mT
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Compare and Contrast the motion of charged
particles in electric and magnetic fields
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Sample Problem - Electrons switch direction

• Calculate the force and describe the path of this
  electron.

B 2000 mT
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Sample problem

• How would you arrange a magnetic field and an
  electric field so that a charged particle of
  velocity v would pass straight through without
  deflection?
• Think.Pair.Share.

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Electric and Magnetic Fields Together
e-
v E/B
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Free Response

• Split up groups (a,b,c,d)
• Each group completes all
• Random selection for which part to present
• Actually work it out and talk to each other. (No
  Mr. Hayon help)

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What will the path of the charge look like when
subjected to both fields at once?

• Note in this case what is the direction of the
  electric field?
• (Same as the B)

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Sample Problem

• It is found that protons traveling at 20,000 m/s
  pass undeflected through the velocity filter
  below. What is the magnitude and direction of the
  magnetic field between the plates?

20,000 m/s
e
0.02 m
400 V
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Sample Problem

• It is found that protons traveling at 20,000 m/s
  pass undeflected through the velocity filter
  below. What is the magnitude and direction of the
  magnetic field between the plates?

20,000 m/s
e
0.02 m
400 V
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Make up more problems?
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Monday, April 1, 2007

• Magnetic Force on Current Carrying Wires

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The magnetic force on a current-carrying wire in
a magnetic field

• Charge experiences a magnetic force when moving
  through a magnetic field.
• Current is a flow of charges
• ? A wire will experience a force in a B field
• RHR still applies Direction of the velocity
  will be the direction of the current! ( Charge)

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Magnetic Force on Current-Carrying Wire

• F I L B sin?
• I current in Amps
• L length in meters
• B magnetic field in Tesla
• ? angle between current and field
• B is the strength of the external magnetic

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Sample Problem

• What is the force on a 100 m long wire bearing a
  30 A current flowing north if the wire is in a
  downward-directed magnetic field of 400 mT?

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Sample Problem

• What is the force on a 100 m long wire bearing a
  30 A current flowing north if the wire is in a
  downward-directed magnetic field of 400 mT?

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Sample Problem

• What is the magnetic field strength if the
  current in the wire is 15 A and the force is
  downward and has a magnitude of 40 N/m? What is
  the direction of the current?

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Sample Problem

• What is the magnetic field strength if the
  current in the wire is 15 A and the force is
  downward and has a magnitude of 40 N/m? What is
  the direction of the current?

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Magnetic Fields

• Affect moving charge
• F qvBsinq
• F ILBsinq
• Hand rule is used to determine direction of this
  force.
• Caused by moving charge!

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You Try!

• A copper rod 0.150 m long and with a mass of
  0.0500 kg is suspended from two thin, flexible
  wires, as shown in the sketch. At right angles to
  the rod is a uniform magnetic field of 0.550 T
  pointing into the page. Find (a) the direction
  and (b) magnitude of the electric current needed
  to levitate the copper rod.
• (a) to the right
• (b) 5.95 A

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You Try!

• A copper rod 0.150 m long and with a mass of
  0.0500 kg is suspended from two thin, flexible
  wires. At a right angle to the rod is a uniform
  magnetic field of 0.550 T pointing into the page.
  

(a) Find the direction of the current to
levitate the rod (b) magnitude of the electric
current needed to levitate the copper rod.
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(No Transcript)
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Magnetic Field forLong Straight Wire

• B ?oI / (2?r)
• ?o 4? ? 10-7 T m / A
• magnetic permeability of free space
• I current (A)
• r radial distance from center of wire (m)

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Right Hand Rule for straight currents
i

1. Curve your fingers
2. Place your thumb (which is presumably pretty
   straight) in direction of current.
3. Curved fingers represent curve of magnetic field.
4. Field vector at any point is tangent to field
   line.

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For straight currents
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Sample Problem

• What is the magnitude and direction of the
  magnetic field at point P, which is 3.0 m away
  from a wire bearing a 13.0 Amp current?

P
3.0 m
I 13.0 A
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Tuesday, April 3, 2007

• Exam (Current) grading

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Wednesday, April 4, 2007

• Superposition in Magnetic Fields

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Announcements

• Lunch Bunch today lab
• HW 3 due today.
• HW 4 due tomorrow.
• Lunch Bunch 5 due today as well.
• Physics Bowl exam tentatively scheduled for April
  12
• 1st period will hear speaker April 12

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Principle of Superposition

• When there are two or more currents forming a
  magnetic field, calculate B due to each current
  separately and then add them together using
  vector addition.

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Sample Problem not in packet

• What is the magnitude and direction of the force
  exerted on a 100 m long wire that passes through
  point P which bears a current of 50 amps in the
  same direction?

I2 50.0 A
P
3.0 m
I1 13.0 A
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Sample Problem

• What is the magnitude and direction of the
  electric field at point P if there are two wires
  producing a magnetic field at this point?

I 10.0 A
4.0 m
P
3.0 m
I 13.0 A
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Sample Problem

• Where is the magnetic field zero?

I 10.0 A
7.0 m
I 13.0 A
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Thursday, April 5, 2007

• Solenoids

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Announcements

• HW 4 due today
• Problem 47
• HW 5 due Monday
• Physics Bowl Thursday, 2nd in A-180
• Review sessions (715-745 AM all next week)

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In the 4th Grade

• You learned that coils with current in them make
  magnetic fields.
• The iron nail was not necessary to cause the
  field it merely intensified it.

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Solenoid

• A solenoid is a coil of wire.
• When current runs through the wire, it causes the
  coil to become an electromagnet.
• Air-core solenoids have nothing inside of them.
• Iron-core solenoids are filled with iron to
  intensify the magnetic field.

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Magnetic Field Inside aSolenoid

• B ?on I
• ?o 4? ? 10-7 T m / A
• n number of coils per unit length
• I current (A)
• You are not required to memorize this formula,
  but only to use it.

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Magnetic Field around Curved Current
B
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Right Hand Rule for magnetic fields around curved
wires

1. Curve your fingers.
2. Place them along wire loop so that your fingers
   point in direction of current.
3. Your thumb gives the direction of the magnetic
   field in the center of the loop, where it is
   straight.
4. Field lines curve around and make complete loops.

B
I
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Sample Problem

• An air-core 10 cm long is wrapped with copper
  wire that is 0.1 mm in diameter. What must the
  current be through the wire if a magnetic field
  of 20 mT is to be produced inside the solenoid?

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Sample Problem

• What is the direction of the magnetic field
  produced by the current I at A? At B?

I
A
B
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Magnetic Field around Curved Current
B
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Sample Problem

• What is the magnetic field inside the air-core
  solenoid shown if the resistance of the copper
  wire is assumed to be negligible? There are 100
  windings per cm. Identify the north pole.

120 V
I
100-W
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Monday, April 9, 2007

• Work day

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Tuesday, April 10, 2007

• Magnetic Flux

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Announcements

• To be exempt from Lunch Bunch this week
• Give me your classwork packet with free response
  attempt. I will return to you youll correct it
  based on on-line solutions.
• Let me initial your AP review packet.
• Review sessions are ongoing. I will be doing a
  review session tomorrow AM, not lunch bunch.
• Tonight do assignment 6
• Pass forward 5
• Physics Bowl Thursday, Portable 1B. All other
  students go to Moreno.

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Magnetic Flux

• The product of magnetic field and area.
• Can be thought of as a total magnetic effect on
  a coil of wire of a given area.

B
A
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Maximum Flux

• The area is aligned so that a perpendicular to
  the area points parallel to the field

B
A
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Minimum Flux

• The area is aligned so that a perpendicular to
  the area points perpendicular to the field

B
A
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Intermediate Flux

• The area is neither perpendicular nor is it
  parallel

B
A
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Magnetic Flux

• FB B A cos?
• FB magnetic flux in Webers (Tesla meters2)
• B magnetic field in Tesla
• A area in meters2.
• ? the angle between the area and the magnetic
  field.
• FB B?A

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Sample Problem

• Calculate the magnetic flux through a rectangular
  wire frame 3.0 m long and 2.0 m wide if the
  magnetic field through the frame is 4.2 mT.
• Assume that the magnetic field is perpendicular
  to the area vector.
• Assume that the magnetic field is parallel to the
  area vector.
• Assume that the angle between the magnetic field
  and the area vector is 30o.

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Sample Problem

• Assume the angle is 40o, the magnetic field is 50
  mT, and the flux is 250 mWb. What is the radius
  of the loop?

B
A
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Induced Electric Potential

• A system will respond so as to oppose changes in
  magnetic flux.
• A change in magnetic flux will be partially
  offset by an induced magnetic field whenever
  possible.
• Changing the magnetic flux through a wire loop
  causes current to flow in the loop.
• This is because changing magnetic flux induces an
  electric potential.

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Faradays Law of Induction

• e -NDFB/Dt
• e induced potential (V)
• N loops
• FB magnetic flux (Webers, Wb)
• t time (s)

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Wednesday, April 11, 2007

• Faradays Law of Induction

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Announcements

• To be exempt from Lunch Bunch this week
• Give me your class work packet with free response
  attempt. I will return to you youll correct it
  based on on-line solutions.
• Let me initial your AP review packet.
• Last mechanics AP review session tomorrow
  morning. Friday I will host a general session for
  general questions on mechanics.
• Tonight do assignment 7. Tomorrow I will
  collect 6.
• Physics Bowl Thursday, Portable 1B. All other
  2nd period students go to Moreno.
• Mock AP exam Monday night, 630 PM, in cafeteria.
  Only excused absences will be allowed a retake,
  on Thursday morning at 615 AM. Free response
  exams will be given in class, and missing one of
  those will also require a makeup, to be arranged
  with me.

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Faradays Law of Induction

• e -NDFB/Dt
• e induced potential (V)
• N loops
• FB magnetic flux (Webers, Wb)
• t time (s)

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A closer look

• e -DFB/Dt
• e -D(BAcos?)/Dt
• To generate voltage
• Change B
• Change A
• Change ?

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Sample Problem

• A coil of radius 0.5 m consisting of 1000 loops
  is placed in a 500 mT magnetic field such that
  the flux is maximum. The field then drops to zero
  in 10 ms. What is the induced potential in the
  coil?

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Sample Problem

• A single coil of radius 0.25 m is in a 100 mT
  magnetic field such that the flux is maximum. At
  time t 1.0 seconds, field increases at a
  uniform rate so that at 11 seconds, it has a
  value of 600 mT. At time t 11 seconds, the
  field stops increasing. What is the induced
  potential
• A) at t 0.5 seconds?
• B) at t 3.0 seconds?
• C) at t 12 seconds?

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Lenzs Law

• The current will flow in a direction so as to
  oppose the change in flux.
• Use in combination with hand rule to predict
  current direction.

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Sample Problem

• The magnetic field is increasing at a rate of 4.0
  mT/s. What is the direction of the current in the
  wire loop?

118
Sample Problem

• The magnetic field is increasing at a rate of 4.0
  mT/s. What is the direction of the current in the
  wire loop?

119
Sample Problem

• The magnetic field is decreasing at a rate of 4.0
  mT/s. The radius of the loop is 3.0 m, and the
  resistance is 4 W. What is the magnitude and
  direction of the current?

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Thursday, April 12, 2007

• Workday

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Friday, April 13, 2007

• Workday

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Monday, April 16, 2007

• Motional EMF

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Announcement

• Tonights HW 8, due Wednesday.
• Tonight Mock AP in cafeteria. Exam starts at
  630. Bring 2 pencil and eraser. No calculator
  is necessary.
• Tomorrow More of the Mock AP in class.
• Wednesday More of the Mock AP in class.
• Thursday Mock AP makeup at 615 AM. I will be
  here at 600 to set up. Exam starts promptly at
  615 AM.

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Work Time

• Work on Review Packets.
• Work on Exam Corrections.
• Do NOT work on tonights homework!

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Motional emf

• e BLv
• B magnetic field (T)
• L length of bar moving through field
• v speed of bar moving through field.
• Bar must be cutting through field lines. It
  cannot be moving parallel to the field.
• This formula is easily derivable from Faradays
  Law of Induction

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Motional emf - derivation

• e DFB/Dt
• e D(BA) /Dt (assume cosq 1)
• e D(BLx) /Dt
• e BLDx /Dt
• e BLv

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Sample Problem

• How much current flows through the resistor? How
  much power is dissipated by the resistor?

B 0.15 T
50 cm
3 W
v 2 m/s
128
Sample Problem

• In which direction is the induced current through
  the resistor (up or down)?

B 0.15 T
50 cm
3 W
v 2 m/s
129
Sample Problem

• Assume the rod is being pulled so that it is
  traveling at a constant 2 m/s. How much force
  must be applied to keep it moving at this
  constant speed?

B 0.15 T
50 cm
3 W
v 2 m/s
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Lab Magnetic Field Map

• Using a compass, map the magnetic field inside
  and outside your solenoid. Do the following
• Put together 4 sheets of graph paper. Write all
  group members names on paper.
• Trace the solenoid (true size)
• Draw the Compass Rose
• Connect to DC outlet
• Map magnetic field lines with compass
• Draw North and South Poles of solenoid
• Extend field lines through solenoid.