The ratio of kinetic energy to the total energy of an electron in a Bohr orbit of the hydrogen atom, is

The ratio of wavelengths of the last line of Balmer series and the last line of Lyman series is

Radioactive material 'A' has decay constant '8 $$\lambda $$' and material 'B' has decay constant '$$\lambda $$'. Initially they have same number of nuclei. After what time, the ratio of number of nuclei of material 'B' to that 'A' will be e ?

If an electron in a hydrogen atom jumps from the 3^rd orbit to the 2^nd orbit, it emits a photon of wavelength $$\lambda $$. When it jumps from the 4^th orbit to the 3^rd orbit, the corresponding wavelength of the photon will be