The work functions of tungsten and sodium are $5.06 \ eV$ and $2.53 \ eV$ respectively. If the threshold wavelength for sodium is $5896 \ \mathring{A}$,then the threshold wavelength for tungsten will be .......... $\mathring{A}$.

Photoelectric emission takes place from a certain metal at threshold frequency $v$. If the radiation of frequency $4v$ is incident on the metal plate,the maximum velocity of the emitted photoelectrons will be ($m=$ mass of photoelectron,$h=$ Planck's constant).

When radiation of frequency $6 \times 10^{14} \ Hz$ is incident on a metal surface with a work function of $2 \ eV$,the maximum kinetic energy of the emitted photoelectrons is ........ $eV$ (Given: $h = 6.63 \times 10^{-34} \ J \cdot s$,$1 \ eV = 1.6 \times 10^{-19} \ J$). (in $.49$)

$A$ cobalt $(Co)$ plate is placed at a distance of $1 \,m$ from a point source of power $1 \,W$. Assume a circular area of the plate of radius $r = 1 \,Å$ is exposed to the radiation and ejects photoelectrons. The light energy is considered to be spread uniformly and the work function of cobalt is $5 \,eV$. The minimum time the target should be exposed to the light source to eject a photoelectron (assuming no reflection losses) is: (in $\,s$)

The threshold wavelength for photoelectric emission in tungsten is $400 \ nm$. The wavelength of light that must be used in order to eject electrons with a maximum kinetic energy of $0.9 \ eV$ is .............. $nm$.

In photoelectric effect,the graph of stopping potential $(V_0)$ versus frequency $(\nu)$ is a straight line. The slope of this graph is . . . . . . .