1 / 16

Magnetism

Magnetism. Physics 122. Magnetic force on moving charge. Magnetic force F is perpendicular to the velocity v of a particle with charge q F=qvB sin q

aricin
Download Presentation

Magnetism

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. Magnetism Physics 122 Lecture XII

  2. Magnetic force on moving charge • Magnetic force F is perpendicular to the velocity v of a particle with charge q F=qvB sin q • Magnetic field does not change the magnitude of particle’s velocity, only its direction. Charged particles move in circles in constant magnetic field Lecture XII

  3. Magnetic force on moving charge • Circular motion • Magnetic force = Centripetal force F=qvB • Centripetal acceleration a=v2/R • Newton’s second law F=ma qvB=mv2/R In experiments B is known, q=e most of the time, Measure R- measure mv For a given v measure m – magnetic spectrometer Lecture XII

  4. Cyclotron frequency Frequency does not depend on v! For a given particle type (q,m=const) it depends only on B Lecture XII

  5. Particle selector • Crossed E and B fields: • For one given velocity electric force exactly compensates magnetic force • Only particles with this value of velocity emerge from particle selector + + + + - - - - + Lecture XII

  6. Crossed fields • Electric field changes kinetic energy of charged particle qDV=mv2/2 • Magnetic field does not change KE, only direction • Lorentz force: Lecture XII

  7. Torque Lecture XII

  8. Current loop in magnetic field • A=ab – area of the loop • Magnetic field exerts a torque on a loop parallel to the magnetic field: Lecture XII

  9. Current loop in magnetic field • q – angle between magnetic field and a perpendicular to the loop !!! • Magnetic field orients a loop current perpendicular to B. • N loops: Lecture XII

  10. Magnetic moment • Current loop (area A, current I, number of turns N) in constant magnetic field B experiences torque • Define magnetic moment m perpendicular to the plane of the loop • Torque Lecture XII

  11. Magnetic moment • Equilibrium position for current loop is when B is perpendicular to the face of the loop, or when magnetic moment is parallel to B • Inside magnetic field magnetic moments orient parallel to the field • Galvanometer: B is know – measure I Lecture XII

  12. Magnetic field created by currents • Electric currents – moving electric charges - create magnetic field • Stationary electric charges do not create magnetic filed • First right hand rule • Thumb along the current • Wrap your fingers around the wire • fingers show the direction of the magnetic field Lecture XII

  13. Magnetic field created by current • Magnetic field B created by current I at a distance r from the conductoris m0 = 4p 10-7Tm/A- magneticpermeability of free space Lecture XII

  14. Ampere’s Law • In a way similar to Gauss’s law for E and Q • Not flux, integral over closed path • Only component of B parallel to dl contributes to integral Lecture XII

  15. Application of Ampere’s Law • Thick wire of radius R carries current I. What is B(r ) in and outside of the wire? • Current through unit area: • Current through circle radius r<R • Path integral over radius r • Ampere’s law • For r>R – same as thin wire Lecture XII

  16. Practical application: coaxial cable • Cylindrical braid carries return current  magnetic field outside is zero. Lecture XII

More Related