Two photons of energy $2.5 eV$ and $3.5 eV$ fall on a metal surface of work function $1.5 eV$. The ratio of the maximum velocities of the photoelectrons emitted from the metal surface is

$A$ silver sphere of radius $1 \ cm$ and work function $4.7 \ eV$ is suspended from an insulating thread in free space. It is under continuous illumination of $200 \ nm$ wavelength light. As photoelectrons are emitted,the sphere gets charged and acquires a potential. The maximum number of photoelectrons emitted from the sphere is $A \times 10^Z$ (where $1 < A < 10$). The value of $Z$ is:

Maximum velocity of the photoelectron emitted by a metal is $1.8 \times 10^{6} \ m/s$. Take the value of specific charge of the electron as $1.8 \times 10^{11} \ C/kg$. Then the stopping potential in volt is

$A$ certain metallic surface is illuminated with monochromatic light of wavelength $\lambda$. The stopping potential for the photoelectric current for this light is $3V_0$. If the same surface is illuminated with light of wavelength $2\lambda$,the stopping potential is $V_0$. The threshold wavelength for this surface for the photoelectric effect is:

In the photoelectric effect,if the intensity of light is doubled,then the maximum kinetic energy of photoelectrons will become

The work functions for tungsten and sodium are $4.5 \text{ eV}$ and $2.3 \text{ eV}$ respectively. If the threshold wavelength $\lambda_0$ for sodium is $5460 \text{ \AA}$, the value of $\lambda_0$ for tungsten is ............ $\text{ \AA}$.