The ratio of the speed of the electrons in the ground state of hydrogen to the speed of light in vacuum is
$1 / 2$
$2 / 137$
$1 / 137$
$1 / 237$
Hydrogen atom is excited from ground state to another state with principal quantum number equal to $4$. Then the number of spectral lines in the emission spectra will be
Match List $- I$ (Experiment performed) with List $-II$ (Phenomena discovered/associated) and select the correct option from the options given the lists
List $- I$ | List $- II$ |
$(1)$ Davisson and Genner | $(i)$ Wave nature of electrons |
$(2)$ Millikan's oil drop experiment | $(ii)$ Charge of an electron |
$(3)$ Rutherford experiment | $(iii)$ Quantisation of energy levels |
$(4)$ Franck-Hertz experiment | $(iv)$ Existence of nucleus |
Discuss the experimental results of Geiger-Marsden's $\alpha $ -particle scattering.
Apply Bohr’s atomic model to a lithium atom. Assuming that its two $K$-shell electrons are too close to nucleus such that nucleus and $K$-shell electron act as a nucleus of effective positive charge equivalent to electron. The ionization energy of its outermost electron is......$eV$
An electron having de-Broglie wavelength $\lambda$ is incident on a target in a X-ray tube. Cut-off wavelength of emitted $X$-ray is :