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Polarization occurs when a charge is placed next to a conducting object. When we ground the side of the object opposite the charge, that side becomes neutral.
But this neutralization disturbs the previous equilibrium. Thus, more polarization should be induced by the charge on the end of the object next to the charge and so more and more polarization should induced. Why doesn't this happen in the real world?
Let me help you clear your concept first. Consider $-q$ charge placed next to the conductor. Let the side facing the conductor be $A$ and the opposite side be $B$. The $-q$ charge induces a positive surface charge density ($\sigma_A=q/\text{area}$) on surface $A$. Therefore, a negative surface charge density ($\sigma_B=-q/\text{area}$) is induced on surface $B$. When we ground the conductor the electrons will flow to the ground from surface $B$ while the positive charge at surface $A$ remains held there due to the attractive force of the $-q$ charge placed next to the conductor (hence the equilibrium is not disturbed yet). When the grounding wire is removed the conductor gains a permanent positive surface charge density . Therefore polarization, or charge by induction, is stable.
