Let us assume a sinusoidally varying voltage is impressed across the primary with secondary winding open circuited. Although the current drawn Imwill be practically zero, but its position will be 90 lagging with respect to the supply voltage. The flux produced will obviously be in phase with Im . In other words the supply voltage will lead the flux phasor by 90. Since flux is common for both the primary and secondary coils,
The time varying flux φ (t) will link both the primary and secondary turns inducing in voltages e1 and e2 respectively