  The current understanding of the formation of powerful bi-directional jets in
systems such as radio galaxies and quasars is that the process involves a
supermassive black hole that is being fed with magnetized gas through an
orbiting accretion disc. In this paper we discuss the dynamics of the jet
powered by rotating black holes, in the presence of a magnetic field, including
the scaling of the jet length and their typical time scales. We consider a
unified picture covering all phenomena involving jets and rotating black holes
ranging from gamma ray bursts to extragalactic jets and discuss the relevant
scaling laws. We have also discussed the acceleration of the particles in jets
and consequent synchrotron and inverse Compton radiations. Accelerated protons
from jets as possible sources of high energy cosmic rays are also discussed.
