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Physics · PYQ NEET UG 2026
हिन्दीA unit positive point charge is taken slowly through an infinitesimally thin tube that is inside a charged dielectric sphere of radius \( R \), having uniform positive charge density \( \rho \), as shown in the figure. The initial and final positions of the charge are marked by \( A \) and \( B \) at distances \( 2R \) and \( 3R \) respectively, from the centre of the sphere. In this process, the magnitude of the total work done on the point charge is \( \frac{\rho R^2}{n \varepsilon_0} \). The value of \( n \) is : (\( \varepsilon_0 \) is the permittivity of vacuum)
Correct answer · Option 4
18
Explanation
Work done is equal to the negative change in potential energy, \( W = -q (V_B - V_A) \). Using Gauss's law for potentials inside and outside the charged dielectric sphere and integrating, we get \( n = 18 \).
