The work function of a metal is $2.51 eV$. Its threshold frequency is:

The frequency of incident light falling on a photosensitive material is doubled. The kinetic energy $(K.E.)$ of the emitted photoelectrons will be:

In a photoelectric experiment,the stopping potential was measured to be $V_1$ and $V_2$ volts with incident light of wavelength $\lambda$ and $\frac{\lambda}{2}$ respectively. The value of $V_2$ is: [where $\phi=$ work function,$e=$ electronic charge]

$A$ photoelectric surface is illuminated successively by monochromatic light of wavelength $\lambda$ and $\frac{\lambda}{2}$. If the maximum kinetic energy of the emitted photoelectrons in the first case is one-fourth that in the second case,the work function of the surface of the material is ($c=$ speed of light,$h=$ Planck's constant).

The electric field associated with a monochromatic light wave is given by $E = E_0 \sin \left[ \left( 1.57 \times 10^7 \text{ m}^{-1} \right) (x - ct) \right]$. The stopping potential when this light is used in a photoelectric experiment with a metal having a work function of $1.9 \text{ eV}$ is: (Planck's constant,$h = 6.64 \times 10^{-34} \text{ J-s}$) (in $\text{ V}$)

Work function of lithium and copper are respectively $2.3 \ eV$ and $4.0 \ eV$. Which one of the metal will be useful for the photoelectric cell working with visible light? $(h = 6.6 \times 10^{-34} \ J \cdot s, c = 3 \times 10^8 \ m/s)$