Principle of Ac Generator
One method to induce an emf or current in a loop is through a change in the loop orientation or a change in it’s effective area. As the coil rotates in a magnetic field B , the effective area of the loop (the face perpendicular to the field) is AcosӨ, where Ө is the angle between A and B. This method of producing a flux change is the principle of operation of a simple ac generator.
IF YOU ARE SATISFIED DO GIVE THUMBS UP. (Do not Consider the diagram ,its only for your understanding)