When light of wavelength '$\lambda$' is incident on a photosensitive surface, the stopping potential is 'V'. When a light of wavelength $1.5\lambda$ is incident on the same surface, the stopping potential is '$\dfrac{V}{4}$'. Threshold wavelength for the surface is

If the ionisation energy for the hydrogen atom is $13.6$ eV, then the energy required to excite it from the ground state to the next higher state is nearly

The de-Broglie wavelength of an electron moving in the $n^{th}$ Bohr orbit of radius 'r' is

The magnetic moment of electron due to orbital motion is proportional to
($n$ = principal quantum number)