why are only four lines visible for hydrogen when calculations show many possible emission lines?

Question

why are only four lines visible for hydrogen when calculations show many possible emission lines?

Answer 1

The key word here is "visible." The human eye is only sensitive to light with wavelength between about 400 and 700 nm. If you calculate the emission spectrum of hydrogen, you will find that only four emission lines have wavelengths in this range. The other emission lines either have wavelengths that are too long or too short to be seen by the human eye. However, they can be detected by devices that are sensitive to different wavelengths of light.