1 / 33

PHYS 270 – SUPPL. #4

PHYS 270 – SUPPL. #4. DENNIS PAPADOPOULOS FEBRUARY 2, 2009. OVERVIEW. COMPARE E-FIELD TO B-FIELD PROPERTIES FIELDS, FIELD LINES, DIPOLES COMPUTE B-FIELDS DUE TO CURRENTS BIOT-SAVART, LONG WIRES, CURRENT LOOPS, SOLENOIDS AMPERE’s LAW – EQUIVALENCE TO GAUSS’s LAW

haracha
Download Presentation

PHYS 270 – SUPPL. #4

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. PHYS 270 – SUPPL. #4 DENNIS PAPADOPOULOS FEBRUARY 2, 2009

  2. OVERVIEW • COMPARE E-FIELD TO B-FIELD PROPERTIES • FIELDS, FIELD LINES, DIPOLES • COMPUTE B-FIELDS DUE TO CURRENTS • BIOT-SAVART, LONG WIRES, CURRENT LOOPS, SOLENOIDS • AMPERE’s LAW – EQUIVALENCE TO GAUSS’s LAW • MAGNETIC FORCES ON MOVING CHARGES • MAGNETIC PROPERTIES OF MATTER - MRI

  3. Magnetic Forces

  4. Work due to magnetic force on a charged particle

  5. MAGNETIC FORCES ON CHARGES Do the B forces do work? e.g. qF=1/2 (mv2) Magnetic force acts to change the direction of v but not the magnitude or the value of the force Centripetal acceleration

  6. PARTICLE ORBITS VAN ALLEN BELTS

  7. FORCES ON WIRES a

  8. FORCES ON WIRES a

  9. Attraction Repulsion MUTUAL LOOP FORCES m

  10. Summary Forces on Charges and Currents Attraction Repulsion

  11. SOLENOIDS What is a solenoid – A device that creates a uniform magnetic field inside and zero outside (in both cases almost uniform and almost zero) Who needs it . Electronic devices, MRI machines, Fusion machines etc

  12. How to make a solenoid

  13. B FIELD INSIDE A SOLENOID n is turns per unit length (e.g. per meter)

  14. MAGNETIC TORQUE

  15. TORQUE ON CURRENT LOOPS

  16. ELECTRIC MOTORS Armature is a coil

  17. MAGNETIC PROPERTIES OF MATTER How does a magnet picks up metal paper clips ? Why not plastic ? How is it different from a charged comb picking up pieces of paper ?

  18. Paired (diamagnetic) repelled by B Mutual cancellation No net m Unpaired (paramagnetic) attracted by B Ferromagnetic

  19. 1. Electrons are microscopic magnets due to their spin 2. Ferromagnetic materials are organized in spin aligned domains 3. In external B produce induced magnetic dipole moment Hysteresis

  20. MRI BODY CONTAINS MAINLY WATER MOLECULES, EACH CONTAINING TWO HYDROGEN ATOMS(TWO PROTONS). IN A STRONG UNIFORM MAGNETIC FIELD THE MAGNETIC MOMENTS OF THE PROTONS ALIGN WITH THE B-FIELD. WHEN A RADIO-FREQUENCY EM FIELD IS TURNED ON THEY ABSORB SOME ENERGY AND GIVE IT BACK WHEN IT IS TURNED-OFF. DESEASED TISSUE, SUCH AS TUMORS, IS DETECTED BECAUSE THE RELAXATION RATE ( RETURN TO EQUILIBRIUM) DEPENDS ON THE TISSUE.

More Related