When the distance of separation between the slit and screen is doubled, the angular separation between fringes in single slit diffraction pattern experiment

Light of wavelength $\lambda$ is incident on a single slit of width 'a' and the distance between slit and screen is D. In diffraction pattern, if slit width is equal to the width of the central maximum then D is equal to

Light of wavelength '$\lambda$' which is less than threshold wavelength is incident on a photosensitive material. If incident wavelength is decreased so that emitted photoelectrons are moving with some velocity then stopping potential

When the electron orbiting in hydrogen atom in its ground state moves to the third excited state, the de-Broglie wavelength associated with it