Ever since we all know about the ordinary clock, which uses the constant periodic to and fro motion of the pendulum to control movement of hands of clock or digits of the face of clock. Now we can think in terms of atom because the Atomic Clock utilizes the oscillations of the atom to determine time. It consists of electronic amplifier in the microwave cavity. The elements of cavity like Hydrogen, Cesium and Rubidium are heated to release charge containing atoms. When low energy atom can change to a high energy atom it is passed through magnetic field only if it oscillating at needed frequency. These oscillations are converted to a pulse of one second and then there comes the Atomic clock.