The wavelength of light in the visible region is about 390 nm for violet colour. The energy of photons in (eV) is:

$\left(\mathrm{Take} \mathrm{h}=6.63\times {10}^{-34} \mathrm{Js}, \mathrm{and} 1 \mathrm{eV}=1.6\times {10}^{-19} \mathrm{J}\right)$

1. 1.64 eV

2. 2.26 eV

3. 3.19 eV

4. 4.03 eV

The wavelength of light in the visible region is about 550 nm (average wavelength) for yellow-green colour. Three materials with work functions are given as Al (4.28 eV), Cu (4.65 eV) and Na (2.75 eV). From which of these photosensitive materials, can you build a photoelectric device that operates with visible light?

(1) Al

(2) Cu

(3) Na

(4) None of the above