Field Intensity:

Whenever a coil along with a certain number of ampere-turns is stretched to double its length, the magnetic field intensity, or the concentration of its magnetic lines of force, will be half as great. Thus, field intensity depends on the length of the coil. In the Equation (1-14) is the mathematical representation for field intensity, that is associated to magnetomotive force as display.

 H = F_M / L = NI/L                                  (1-14)

where

H  = field intensity, At/ m

NI = ampere-turns (At)

L   = length between poles of coil (m)

F_M = Magnetomotive force (mmf)

Example:    Find the field intensity of an 80 turn, 20 cm coil, with 6A of current.

Solution:

N = 80, I = 6A, and NI = 480 At

H =     480 At/ 0.2 m= 2400 At/m

Example:    If the similar coil in Example 1 were to be stretched to 40 cm along with wire length and current remaining the similar, find the new value of field intensity.

Solution:

N = 80, I = 6A, and NI = 480 At

H = 480 At/ 0.4 m= 1200 At/m