The magnetomotive force of a coil, F, is obtained by multiplying the number of turns with the current strength.
`F = N*I`
Here, `N = 250, I = 0.4` amperes
So, `F= 250*0.4 = 100`
Magnetic field strength, H, is given by:
`H=(N*I)/l` (where, l is the path length)
Plugging in the values,
`H=100/(20*10^-2) = 500 `
Therefore, the mmf of the coil is 100 ampere-turns, and its magnetic field strength is 500 ampere-turns/meter.