A rectangular iron core has three coils as shown in the given figure. The number of turns of the coils are N_a = 300, N_b = 600 and N_c = 600, and the respective currents are 1.5 A, 4 A and 3 A. Find the total magnetomotive force.

Concept:

The magneto motive force ( MMF ) for a coil having N turns, carrying current I is given by

MMF = N × I  and is responsible for causing the Flux.

The direction of Flux is given by Flemings Right hand curl rule.

Application:

Given:

N_a = 300, I_a = 1.5 A, N_b = 600, I_b = 4 A, N_c = 600, I_c = 3 A

Let us assume direction of flux in upward direction be +ve and downward direction be -ve

For Coil A, MMF_a = N_a I_a = 300 × 1.5 = 450 AT ( + )

For coil B, MMF_b = N_b I_b = 600 × 4 = 2400 AT ( + )

For coil C, MMF_c = N_c I_c = 600 × 3 = 1800 AT ( - )

Net MMF = 450 + 2400 - 1800 = 1050 AT

Note: The direction of flux for coil a and coil b are in same direction and in opposite direction for coil c.