7.8 LC O SCILLATIONS · Part 2

. The oscillations in an LC circuit are analogous to the oscillation of a block at the end of a spring. The figure depicts one-half of a cycle. At t = , the switch is closed and the capacitor starts to discharge [Fig. . (b)]. As the current increases, it sets up a magnetic field in the inductor and thereby, some energy gets stored in the inductor in the form of magnetic energy: U B = ( / ) Li . As the current reaches its maximum value i m , (at t = T / ) as in Fig. . (c), all the energy is stored in the magnetic field: U B = ( / ) Li m . You can easily check that the maximum electrical energy equals the maximum magnetic energy. The capacitor now has no charge and hence no energy. The current now starts charging the capacitor, as in Fig. . (d). This process continues till the capacitor is fully charged (at t = T / ) [Fig. . (e)]. But it is charged with a polarity opposite to its initial state in Fig. . (a). The whole process just described will now repeat itself till the system reverts to its original state. Thus, the energy in the system oscillates between the capacitor and the inductor.