If the least distance of distinct vision for a boy is 35 cm , then the lens to be used by the boy for correcting the defect of his eye is

In Young's double slit experiment, if the distance between the slits is increased to 3 times initial distance, then the ratio of initial and final fringe widths is

A solid of mass 1 kg has $6 \times 10^{24}$ atoms. If one electron is removed from every one atom of $0.005 \%$ of the atoms, then the charge gained by the solid is

One of the two identical capacitors having the same capacitance $C$, is charged to a potential $V_1$ and the other is charged to a potential $V_2$. If they are connected with their like plates together, then the decrease in the electrostatic potential energy of the combined system is