The spatial fluctuation of the stator $\operatorname{mmf} \mathcal{F}_1$ is expressed as
$$
\mathcal{F}_1=F_{1 \text { (peak) })} \cos \theta
$$
where $\theta$ is the electrical angle measured from the stator coil axis and $F_{1 \text { (poak) }}$ is the instantaneous value of the mmf wave at the coil axis and is proportional to the instantaneous stator current. If the stator current is a cosine function of time, the instantaneous value of the spatial peak of the pulsating mmf wave is
$$
F_{1(\text { pask })}=F_{1(\max )} \cos \omega t
$$
where $F_{1(\max )}$ is the peak value corresponding to maximum instantaneous current. Derive the expression for $\mathcal{F}_1$, and verify that for a single-phase winding, both forward and backward components are present.