what are the methods of Methods of producing induced emf

Hence, the induced emf can be produced by changing the magnetic induction  area enclosed by the coil  and  the orientation of the coil (θ) with respect to the magnetic field

and too depends over NBA cos θ

Presently, there are six known methods for producing a voltage or electromotive force (emf). Some of these methods are more widely used than others, and some are used mostly for specific applications. Following is a list of the six known methods of producing a voltage.
1. FRICTION - Voltage produced by rubbing certain materials together.
2. PRESSURE (piezoelectricity) - Voltage produced by squeezing crystals of certain substances.
3. HEAT (thermoelectricity) - Voltage produced by heating the joint (junction) where two unlike metals are joined.
4. LIGHT (photoelectricity) - Voltage produced by light striking photosensitive (light sensitive) substances.
5. CHEMICAL ACTION - Voltage produced by chemical reaction in a battery cell.
6. MAGNETISM - Voltage produced in a conductor when the conductor moves through a magnetic field, or a magnetic field moves through the conductor in such a manner as to cut the magnetic lines of force of the field.