Polarisation — Prelims Strategy

Prelims Strategy

For NEET Prelims, a strong conceptual understanding of polarisation is paramount. Start by clearly differentiating between polar and non-polar molecules and how each responds to an electric field. Memorize the key formulas: $K = 1 + \chi_e$, $E = E_0/K$, $C = KC_0$. Pay special attention to the two crucial scenarios for capacitors with dielectrics:

1
Capacitor connected to a battery (constant voltage $V$) — Here, $V$ remains constant. $E = V/d$ remains constant. $C$ increases by $K$. $Q = CV$ increases by $K$. $U = \frac{1}{2}CV^2$ increases by $K$.
2
Capacitor disconnected from a battery (constant charge $Q$) — Here, $Q$ remains constant. $C$ increases by $K$. $V = Q/C$ decreases by $K$. $E = V/d$ decreases by $K$. $U = Q^2/(2C)$ decreases by $K$.

Practice identifying which quantities remain constant and which change in each scenario. For numerical problems, ensure correct application of the dielectric constant $K$. Trap options often involve confusing these two scenarios or misapplying the factor $K$. Always read the question carefully to determine if the capacitor is isolated or connected to a source. Conceptual questions might ask about the definition of polarisation, the role of bound charges, or the properties of $\chi_e$ and $K$.