Q52 / 75 · JEE Main 2025 (7 Apr Shift 2) · Physics
A parallel plate capacitor has charge $5 \times 10^{-6} \mathrm{C}$. A dielectric slab is inserted between the plates and almost fills the space between the plates. If the induced charge on one face of the slab is $4 \times 10^{-6} \mathrm{C}$ then the dielectric constant of the slab is ________.
Correct answer: 5
Solution
$\begin{aligned} & \mathrm{Q}_{\mathrm{in}}=\mathrm{Q}\left(1-\frac{1}{\mathrm{~K}}\right) \\ & 4 \times 10^{-6}=5 \times 10^{-6}\left(1-\frac{1}{\mathrm{~K}}\right) \\ & 1-\frac{1}{\mathrm{~K}}=\frac{4}{5} \\ & \mathrm{~K}=5\end{aligned}$
Hence, the correct answer is 5.