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Magnetic Field

Magnetic Field. Magnetic Levitation. These express trains in Japan are capable of speeds ranging from 225 ~ 480 km/h. Magnetic Resonance Imaging. A “slice” of human brain. Nature of Magnets.

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Magnetic Field

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  1. Magnetic Field

  2. Magnetic Levitation These express trains in Japan are capable of speeds ranging from 225 ~ 480 km/h

  3. Magnetic Resonance Imaging A “slice” of human brain

  4. 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

  5. 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

  6. Magnetic Field Lines • Magnetic field lines are used to describe magnetic field • Magnetic field lines show both direction and strength of magnetic field

  7. Typical Magnetic Field (1)

  8. Typical Magnetic Field (2)

  9. Similarity of Two Magnetic Fields

  10. The Earth’s Magnetic Poles

  11. First Right|Hand Rule

  12. Second Right-Hand Rule N S

  13. Applications of Electromagnet

  14. Applications of Electromagnet

  15. 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

  16. 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

  17. Increase Strength of Electromagnet • Use iron (steel) core • Increase current (voltage) • Increase wraps of solenoid

  18. Microscopic Picture of Magnets

  19. Magnetic Force

  20. 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

  21. Third Right-hand Rule

  22. Calculate Magnetic Force F = BIL F is in Newton, B is in Tesla, I is in Ampere, and L is in meter

  23. Nature 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. T θ F 0.2 N Steps to Compute Magnetic Force • 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 different

  25. Application of Magnetic Force • Paper cone attached to coil • Sound signal converted to varying electric current

  26. Galvanometer

  27. Electric Motor

  28. 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

  29. Electromagnetic Induction

  30. Electromotive Force (EMF) • EMF should be called electromotive potential • Unit of EMF is Volt • EMF = BLV (maximum value)

  31. Electric Guitar

  32. Tape Recorder

  33. Electric Generator

  34. Difference of Generator and Motor

  35. Effective Current & Effective Voltage Similarly,

  36. 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

  37. Lenz’s Law Illustration

  38. Transformer

  39. 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.

  40. Ignition System

  41. Examples

  42. Example Problem A straight wire 0.20 m moves perpendicularly through 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

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