Two metal plates (A, B) are kept horizontally with separation of $ \left( \frac{12}{\pi} \right) $ cm, with plate A on the top.

An atomizer jet sprays oil (density 1.5 g/cm³) droplets of radius 1 mm horizontally. All oil droplets carry a charge 5 nC. The potentials V_A and V_B are required on plates A and B respectively in order to ensure the droplets do not descend. The values of V_A and V_B are ______.

(Neglect the air resistance to the droplets and take g = 10 m/s²)

Two point charges $8\ \mu C$ and $-2\ \mu C$ are located at $x = 2$ cm and $x = 4$ cm, respectively on the $x$-axis. The ratio of electric flux due to these charges through two spheres of radii 3 cm and 5 cm with their centers at the origin is ________.

One side of an equilateral prism is painted by a transparent material of refractive index $n_2$. The refractive index of prism is $1.6$. The minimum value of $n_2$ required for total internal reflection from painted face is ________.

The figure given below shows an LCR series circuit with two switches S₁ and S₂. When switch S₁ is closed keeping S₂ open, the phase difference (φ) between the current and source voltage is 30° and phase difference is 60° when S₂ is closed keeping S₁ open. The value of (3L₁ − L₂) is ______ H.