2
Magnetic LevitationMagnetic Levitation
These express trains in Japan are capable of speeds
ranging from 225 ~ 480 km/h
4
Nature of MagnetsNature of Magnets
1.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
5
Properties of Magnetic Properties of Magnetic FieldField
• 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
6
Magnetic Field LinesMagnetic Field Lines
• Magnetic field lines are used to describe magnetic field
• Magnetic field lines show both direction and strength of magnetic field
15
How to Calibrate the How to Calibrate the SensorSensor
• 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 SensorHow 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
17
Increase Strength of Increase Strength of ElectromagnetElectromagnet
1.Use iron (steel) core2.Increase current
(voltage)3.Increase wraps of
solenoid
20
Measure of Magnetic FieldMeasure 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
22
Calculate Magnetic ForceCalculate 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 ForceNature of Magnetic Force
F is the resultant force that magnetic field exerts on all moving charges
F = BIL => I = q/t => t = L/v=> I =q/t = qv/L
=> F = B(qv/L)L = Bqv
24
Steps to Compute Magnetic Steps to Compute Magnetic ForceForce
• Measure distance the pipe moved
• Compute θ 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 differentθ
T
F
0.2 N
25
Application of Magnetic Application of Magnetic ForceForce
• Paper cone attached to coil
• Sound signal converted to varying electric current
28
Key Procedures to Build a Key Procedures to Build a MotorMotor
• 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
30
Electromotive Force (EMF)
• EMF should be called electromotive potential
• Unit of EMF is Volt• EMF = BLV (maximum value)
36
Effective Current & Effective Voltage
maxmax21
max2
212
2
21
max21
707.0 III
RIRI
RIP
PPP
eff
eff
DCAC
Similarly,
maxmax21 707.0 VVVeff
37
Lenz’s 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
40
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.