Chapter 19   Magnetism

 Magnetic Field and Magnetic Force

 

  • Electric field is produced by electric charges.
  • Electric force is the force experienced by an electric charge.
  • Magnetic field (B) is produced by electric currents (I).
  • Magnetic force is experienced by a current (or a moving charge).

 Empirical I-B Relationships

B-Field Produced at a distance 'r' from a Line Current I

B = (mo/2p) I/r

where B in Tesla, I in Amp, r in meter and mo = 4p x10**-7 (T. m/A) is the permeability in free space.

The direction of B is determined by the right-hand rule: Point the thumb of the right-hand in the direction of the current I, the fingers curl in the direction of the B-field produced by the current.

B-Field Produced at the Center of a Circular Current Loop

B = (mo/2) (I/R)

where R is the radius of the circular current loop, I is the current flowing on the loop.

 

 

Solenoids

A solenoid is a coil of N closely-wrapped turns of radius R carrying a current I.  Solenoid is a circuit element capable of storing magnetic energy.

The magnetic field inside a solenoid of N turns and length L can be approximated empirically by                                  
                                              B = mo (N/L) I = mo n I

Ampere's Law

S (B|| Dl) = mo S I

           B|| = component of B parallel to a path element    
           Dl = path element
           I = current enclosed by the path                              

Apply Ampere's Law to Two Examples

  • An Infitely long Line Current (see Figure 19.24 and the calculation)
  • An Infinitely Long Solenoid (see Figure 19.25 and the calculation)

 

HW Chap19:  P9,  P22,  P33,  P63,  P69,  P79