Write different methods to produce induced $emf$.

(N/A) Induced $emf$ can be produced by changing the magnetic flux linked with a coil. The magnetic flux is given by $\phi = AB \cos \theta$. Therefore,the flux can be changed by the following methods:
$(1)$ By changing the magnetic field induction $\vec{B}$.
$(2)$ By changing the area of the coil $A$.
$(3)$ By changing the angle $\theta$ between the area vector $\vec{A}$ and the magnetic field vector $\vec{B}$.