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3.2.1.     Magnetic Fields   <CJ chap 21.1-21.6  >

3.2.1.1. Discussion

3.2.1.1.1.     General discussion of magnetism, N & S poles, magnetic field lines, earths magnetic field, direction N

3.2.1.1.2.     Motion of a charged particle in a magnetic field – Right Hand Rule

3.2.1.1.2.1. Cosmic rays to earth go to poles thus protecting the earth from this radiation

3.2.1.1.3.     The units of the magnetic field are the Tesla = Nt/(C m/s). One Tesla is a very intense magnetic field

3.2.1.1.3.1. The Gauss is defined by 1 T = 10⁴ G.  The earth’s magnetic field is about ½ G.

3.2.1.1.4.     This force on a current segment in a magnetic field opens up the possibility of the motor

3.2.1.2. Mathematical

3.2.1.2.1.     Magnetic Force on a moving charge is  F = q v x B  =  q v B sin  

3.2.1.2.2.     Magnetic force on a current segment   DF = I Dr x B 

3.2.1.2.3.     Magnetic dipole moment defined:   m = I A where I = current in a loop of  area A

3.2.1.2.3.1. Torque t on a magnetic dipole m in a magnetic field B is  t = m x B

3.2.1.2.3.2. The potential energy of a magnetic dipole in a magnetic field is  U = - m  B

3.2.1.2.4.     Radius & Period of the path of a charged particle in a magnetic field r = mv/qB  T=2pm/qB

3.2.1.3. Advanced

3.2.1.3.1.     Magnetic force on a current segment  dF = I dr x B  where I = the current in amps

3.2.1.3.1.1. Derivation: dF = dq (dr/dt) x B then divide dq by dt to get current I leaving dr