Magnetic Field

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Magnetic Field
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Magnetic Levitation
These express trains in Japan are capable of
speeds ranging from 225 480 km/h
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Magnetic Resonance Imaging

• A slice of human brain

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Nature of Magnets

• A magnet can be split into two or more magnets
  and each of them has N and S poles which cannot
  be isolated
• 2. This tells the nature of a magnet All
  properties of a magnet come from electric current
  loops

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Properties of Magnetic Field

• Magnetic field is a special type of matter
• Magnetic field contains energy
• Interaction between magnetic field and electric
  current (electric field)
• Magnetic field strength and direction

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Magnetic Field Lines

• Magnetic field lines are used to describe
  magnetic field
• Magnetic field lines show both direction and
  strength of magnetic field

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Typical Magnetic Field (1)
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Typical Magnetic Field (2)
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Similarity of Two Magnetic Fields
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The Earths Magnetic Poles
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First RightHand Rule
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Second Right-Hand Rule
N
S
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Applications of Electromagnet
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Applications of Electromagnet
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How to Calibrate the Sensor

• Turn FINE control to mid-rotation position
• Press RUN/20K button, allow a few seconds or the
  unit to stabilize
• Zero display using OFFSET knob unless display
  shows under 0.05 or so
• Select 2K range and zero display using COARSE
  control
• Select 200 range and zero display using FINE
  control

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How to Use the Sensor

• Choose larger range of measurement if no reading
• Rotate the probe slightly to get peak reading
• Press STOP to turn off the unit

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Increase Strength of Electromagnet

1. Use iron (steel) core
2. Increase current (voltage)
3. Increase wraps of solenoid

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Microscopic Picture of Magnets
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Magnetic Force
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Measure of Magnetic Field

• Magnetic induction, B, is the identity to
  describe a magnetic field
• B is a vector so it has magnitude and direction
• Unit Tesla or Gauss 1 Tesla 104 Gauss

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Third Right-hand Rule
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Calculate Magnetic Force
F BIL
F is in Newton, B is in Tesla, I is in Ampere,
and L is in meter
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Nature of Magnetic Force

• F is the resultant force that magnetic field
  exerts on all moving charges
• F BIL gt I q/t gt t L/v
• gt I q/t qv/L
• gt F B(qv/L)L Bqv

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Steps to Compute Magnetic Force

• Measure distance the pipe moved
• Compute ? and F in reference of the FBD
• Measure B and L
• Compute F by F BIL
• Compare the two Fs
• What makes the two Fs different

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Application of Magnetic Force

• Paper cone attached to coil
• Sound signal converted to varying electric current

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Galvanometer
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Electric Motor
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Key Procedures to Build a Motor

• Make wire about 1 m long
• Remove coating on only ONE and SAME side of the
  straight parts of the wire
• Do not set the current greater than 1 amp

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Electromagnetic Induction
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Electromotive Force (EMF)

• EMF should be called electromotive potential
• Unit of EMF is Volt
• EMF BLV (maximum value)

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Electric Guitar
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Tape Recorder
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Electric Generator
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Difference of Generator and Motor
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Effective Current Effective Voltage
Similarly,
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Lenzs Law
The direction of the induced current is such that
the magnetic field resulting from the induced
current oppose the change in the field that cause
the induced current.
Result opposes cause
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Lenzs Law Illustration
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Transformer
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How Can EMF Be Induced?

• If and only if there is a changing magnetic field
  around the conductor or circuit. Movement of
  either the magnetic field or the conductor
  (circuit) is not necessary.

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Ignition System
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Examples
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Example Problem
A straight wire 0.20 m moves perpendicularly throu
gh a magnetic field of magnetic induction 0.008 T
at a speed of 7.0 m/s. What EMF is induced in
the wire?
Solution EMF BLv (0.008 T)(0.2
m)(7 m/s) 0.11 V