An electron in a hydrogen atom revolves around its nucleus with a speed of $6.76 \times 10^6 \mathrm{~ms}^{-1}$ in an orbit of radius $0.52 \mathrm{~A}^{\circ}$. The magnetic field produced at the nucleus of the hydrogen atom is _________ T.

The fundamental frequency of vibration of a string stretched between two rigid support is $50 \mathrm{~Hz}$. The mass of the string is $18 \mathrm{~g}$ and its linear mass density is $20 \mathrm{~g} / \mathrm{m}$. The speed of the transverse waves so produced in the string is ___________ $\mathrm{ms}^{-1}$

In the given figure the total charge stored in the combination of capacitors is $100~ \mu \mathrm{C}$. The value of ' $x$ ' is _________.

As per given figure $A, B$ and $C$ are the first, second and third excited energy levels of hydrogen atom respectively. If the ratio of the two wavelengths $\left(\right.$ i.e. $\left.\frac{\lambda_{1}}{\lambda_{2}}\right)$ is $\frac{7}{4 n}$, then the value of $n$ will be __________.