What does the variable "k" mean in the solenoid equation in the picture attached? Many thanks for the help. enter image description here

Source: Theory & Practice of Electromagnetic Design of DC Motors & Actuators

George P. Gogue & Joseph J. Stupak, Jr.

  • 1
    \$\begingroup\$ Link to the original document? \$\endgroup\$
    – Andy aka
    Mar 9, 2018 at 0:40
  • \$\begingroup\$ consult-g2.com/course/chapter11/chapter.html \$\endgroup\$
    – Martin K
    Mar 9, 2018 at 0:56
  • 1
    \$\begingroup\$ @MartinK The equations are immediately above the curve. Can't you guess, just by inspection, the implied meaning of \$k\$? Just look up slightly and I think you can see the factors in play there. (Nice page, by the way.) \$\endgroup\$
    – jonk
    Mar 9, 2018 at 2:00
  • \$\begingroup\$ See the link, equations 11.41 and 11.50. \$\endgroup\$ Mar 9, 2018 at 3:37
  • \$\begingroup\$ so k=Uo/2*Ag*n^2*i^2 ??? Sorry but I am not good at maths :) \$\endgroup\$
    – Martin K
    Mar 9, 2018 at 5:07

1 Answer 1


This might help: -

Force = \$(N\cdot I)^2\cdot 4\pi 10^{-7}\cdot \dfrac{A}{2g^2}\$

  • F = Force
  • I = Current
  • N = Number of turns
  • g = Length of the gap between the solenoid and the magnetizable metal
  • A = Area

If current, area and turns are constant, Force is inversely proportional to the gap squared (\$\ell^2\$). Formulas taken from this question.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.