(a) The jurisdiction of the judges of the superior courts is coextensive with the limits of this state; they may act in circuits other than their own when authorized by law, but they are not compelled to alternate unless required by law.

(b) The authority granted in subsection (a) of this Code section to each judge in his own circuit may be exercised by any judge of another circuit whenever the resident judge is absent from the circuit so that the business thereof cannot be done as speedily as necessary, or is indisposed, or is interested in a case, or is laboring under any disqualification or inability to serve, or in case the circuit is, from any cause, without a judge. The grounds for the exercise of such authority should be shown.