In a certain region of the screen, number of fringes formed is observed to be 8 in Young's double slit experiment when light of wavelength $6600\ \text{Å}$ is used. If the light of wavelength $4400\ \text{Å}$ is used, the number of fringes observed in the same region of the screen will be

In a Fraunhofer diffraction of a single slit, when a slit is illuminated by a light of wavelength $6480\ \text{Å}$, angular width of central maximum is measured. When the slit is illuminated by light of another wavelength '$\lambda$' the angular width decreases by $25\%$. The value of $\lambda$ in $\text{Å}$ units is

If the kinetic energy of a particle is increased to 16 times, the percentage change in the de Broglie wavelength of a particle is

In case of photoelectric emission from certain metal, the cutoff frequency is $\nu$. If the radiation of frequency $3\nu$ is incident on the metal plate, the maximum possible velocity of the emitted electrons will be ($m$ = mass of electron, $h$ = Planck's constant)