Magnetic FieldMagnetic Field

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Magnetic LevitationMagnetic Levitation

These express trains in Japan are capable of speeds

ranging from 225 ~ 480 km/h

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Magnetic Resonance ImagingA “slice” of human brain

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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

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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

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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

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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 Earth’s Magnetic PolesThe Earth’s Magnetic Poles

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Second Right-Hand RuleSecond Right-Hand Rule

N S

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Applications of Applications of ElectromagnetElectromagnet

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Applications of Applications of ElectromagnetElectromagnet

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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

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Increase Strength of Increase Strength of ElectromagnetElectromagnet

1.Use iron (steel) core2.Increase current

(voltage)3.Increase wraps of

solenoid

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Microscopic Picture of Microscopic Picture of MagnetsMagnets

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Magnetic ForceMagnetic Force

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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

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Third Right-hand RuleThird Right-hand Rule

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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

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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

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Application of Magnetic Application of Magnetic ForceForce

• Paper cone attached to coil

• Sound signal converted to varying electric current

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GalvanometerGalvanometer

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Electric MotorElectric Motor

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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

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Electromagnetic Electromagnetic

InductionInduction

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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 Difference of Generator and MotorMotor

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Effective Current & Effective Voltage

maxmax21

max2

212

2

21

max21

707.0 III

RIRI

RIP

PPP

eff

eff

DCAC

Similarly,

maxmax21 707.0 VVVeff

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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

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Lenz’s 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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Example Problem

A straight wire 0.20 m moves perpendicularlythrough 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