Question: Q. 2. A sphere $S_{1}$ of radius $r_{1}$ encloses a net charge Q. If there is another concentric sphere $S_{2}$ of radius $r_{2}\left(r_{2}>r_{1}\right)$ enclosing charge $2 Q$, find the ratio of the electric flux through $S_{1}$ and $S_{2}$. How will the electric flux through sphere $S_{1}$ change, if a medium of dielectric constant $K$ is introduced in the space inside $S_{2}$ in place of air?
U] [Comptt. O.D. I, II, III 2014]
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Solution:
Ans. Ratio of electric flux through spheres $S_{1}$ and $S_{2} 1$ Change of electric flux through sphere $S_{1}$
Flux through $S_{1}, \quad \phi_{1}=\frac{Q}{\varepsilon_{0}}$
Flux through $S_{2}, \quad \phi_{2}=\frac{Q+2 Q}{\varepsilon_{o}}=\frac{3 Q}{\varepsilon_{0}}$ No change in the flux through $S_{1}$ with dielectric medium inside the sphere $S_{2}$.
[CBSE Marking Scheme, 2014]
