Light of wavelength $4000 \,\mathring A$ falls on a photosensitive metal and a negative $2 \,V$ potential stops the emitted electrons. The work function of the material (in $eV$) is approximately $(h = 6.6 \times 10^{-34} \,Js, \,e = 1.6 \times 10^{-19} \,C, \,c = 3 \times 10^8 \,m/s)$.

In a photoelectric experiment,the wavelength of the light incident on a metal is changed from $300\, nm$ to $400\, nm$. The decrease in the stopping potential is close to ................ $V$ $\left( \frac{hc}{e} = 1240\, nm \cdot V \right)$

In a photoelectric emission experiment,the stopping potential for a given metal is $V$ volt,when radiation of wavelength $\lambda$ is used. If radiation of wavelength $2 \lambda$ is used with the same metal,then the stopping potential (in volt) will be. [Given: $c = \text{velocity of light}$,$e = \text{charge on electron}$,$h = \text{Planck's constant}$]

In a photoemission experiment,the maximum kinetic energies of photoelectrons from metals $P, Q$ and $R$ are $E_P, E_Q$ and $E_R$,respectively,and they are related by $E_P = 2E_Q = 2E_R$. In this experiment,the same source of monochromatic light is used for metals $P$ and $Q$,while a different source of monochromatic light is used for metal $R$. The work functions for metals $P, Q$ and $R$ are $4.0 \ eV$,$4.5 \ eV$ and $5.5 \ eV$,respectively. The energy of the incident photon used for metal $R$,in $eV$,is:

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 ............ $\text{ \AA}$.

The threshold wavelength for the photoelectric effect on sodium is $5000 \ Å$. Its work function is: