The wavelength of light in the visible region is about 390 nm for violet colour. The energy of photons in (eV) is:
(Take \(h=6.63\times 10^{-34}~\mathrm{Js}\) and \(1\mathrm{eV}=1.6\times 10^{-19}~\mathrm{J}\))

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 \(550~\text{nm}\) (average wavelength) for yellow-green colour. Three materials with work functions are given as \(Al~(4.28~\text{eV}),\) \(Cu~(4.65~\text{eV})\) and \(Na~(2.75~\text{eV}).\) 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