The energy of an electron in the ground state of hydrogen atom is -13.6 eV . The kinetic and potential energy of the electron in the first excited state will be

A Young's double-slit experimental set up is kept in a medium of refractive index $\left(\frac{4}{3}\right)$. Which maximum in this case will coincide with the $6^{\text {th }}$ maximum obtained if the medium is replaced by air?

The potential energy between two nucleon's inside a nucleus is minimum at a distance of about

A pure Si crystal having $5 \times 10^{28}$ atoms $\mathrm{m}^{-3}$ is dopped with 1 ppm concentration of antimony. If the concentration of holes in the doped crystal is found to be $4.5 \times 10^9 \mathrm{~m}^{-3}$, the concentration (in $\mathrm{m}^{-3}$ ) of intrinsic charge carriers in Si crystal is about