Identify the region of the electromagnetic spectrum for the spectral lines when electron transition takes place from higher energy levels to $n=3, 4, 5$ in the atomic spectrum of hydrogen.

It is observed that characteristic $X$-ray spectra of elements show regularity. When frequency to the power '$n$' i.e.,$v^{n}$ of $X$-rays emitted is plotted against atomic number '$Z$',the following graph is obtained. The value of '$n$' is

Mercury street lights emit light of a pale blue color with a wavelength of $436 \, nm$. Calculate its frequency.

Which of the following series of emission spectral lines for hydrogen is observed in the visible region?

What is the intensity of radiation?

In the photoelectric effect,the saturation photocurrent: