Unformatted text preview: Exam II: Thursday, March Magnetics 1st Big Picture Electrostatics Circuits I=  Qo  e = I oe RC t t Review recitations next week (NO QUIZ) Practice Exam on LONCAPA posted now LON RC Circuit Discharge: Time Constant : = RC Q = Qo e  tf Magnetics Charge: Q = Qf 1 e  t I= R e  t = I oe  t Chapter 27: Magnetic Force on Charges and Currents Chapter 28: Sources of Magnetic Field Chapter 29: Electromagnetic Induction Chapter 30: Self Inductance and Inductors Optics 1 Friday, 23 February 2007 2 Friday, 23 February 2007 Magnetic Force Empirically, it is determined that: Fmag = qv B B is the magnetic field experienced by the charge q and has SI units of Tesla (T). Cross Product Review C = A B = B A Magnitude: 1T = 1 N/C N s N = = m/s m C A m 104 tesla q=0 v=0 F =0 F =0 C = AB sin is the angle between A and B 1 Gauss = vB F =0 0.5 G: Magnetic field of Earth 50 T: Maximum DC magnetic field strength 65 T: Maximum pulse field strength F v&B C is perpendicular to both A and B Direction of C is found using the Right Hand Rule! ^ i C = A B = Ax Bx Friday, 23 February 2007 Calculate rigorously: Read more at http://www.magnet.fsu.edu http://www.magnet.fsu.edu Friday, 23 February 2007 3 ^ j Ay By ^ k (Ay Bz  Az B y ) i^  j Az = ( Ax Bz  Az Bx ) ^ + ^ Bz (Ax B y  Ay Bx ) k 4 1 Question Given the situation at the instant shown below, the acceleration of the electron is: Motion of a Charge in an Uniform Magnetic Field y B F = qv B vx, y x RHR ^ F in  k vx , y +q v B F =0 ^ F in k v = constant ^ a in k 2 v r A. B. C. D. E. To the right Up Down Into the page Out of the page v z y F = qv B F = qv B 2 v r Circular motion : Fc = mac = m z v qv B = m qrB = mv = p (momentum!) a Circular motion : = v r qrB = mr = = 2f Friday, 23 February 2007 5 Friday, 23 February 2007 f = qB 2m qB m Cyclotron Frequency! 6 Question A point charge of (+q) enters a region of uniform (+q Bfield as shown. What is its trajectory? A. Circle in the xy plane B. Circle in the yz plane C. Helix traveling in the xxdirection D. Helix traveling in the yydirection E. Helix traveling in the zzdirection y Question A point charge of (+q) enters a region of uniform (+q Bfield as shown. What is its kinetic energy as compared to before entering the Bfield? BA. Bigger B. x y B B v q z Smaller v q z x C. The same Friday, 23 February 2007 7 Friday, 23 February 2007 8 2 Magnetic Force on a Icarrying Wire Fmag = qv B Magnetic Force on a Curved Icarrying Wire F = qv B y I d B d dF y dq x F = nqA vd B Q = nqA dF dF = (dq )v B d = dq B dt dq = d B dt dF = Id B v= d dt dF = Id B B d = I B R v = vd I = nqvd A Friday, 23 February 2007 x dF = Id B d R F= d = Rd  sin i^ + cos ^ j 9 Friday, 23 February 2007 ( ) )( ^ =  IRBd (cos i + sin ^ ) j ^ j dF =  IRB (cos i + sin ^ ) d ^ =  IRB[sin i  cos ^ ] j =  IRB[(0) i^  ( 1  1) ^ ] j ( 0 ^ ^ = IRd  sin i + cos ^  B k j ) 0 = 2 IRB ^ j 10 3 ...
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 Fall '07
 JapGuy
 Magnetic Force, Magnetic Field

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