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## QuestionPhysicsClass 12

The wavelength of light in the visible region is about $$390\; \mathrm{mm}$$ for violet colour, about $$550\; \mathrm{mm}$$ $$($$average wavelength$$)$$ for yellow-green colour and about $$760 \;\mathrm{mm}$$ for red colour.
From which of the photosensitive materials with work functions listed in table and can you build a photoelectric device that operates with visible light?

For a photoelectric device to operate, the condition that must be satisfied is that the energy of the incident light should be greater than or equal to the work function of the material used in the fabrication of the device.
Considering standard table;
When using violet light with incident energy,   $$E_1=3.19\;\mathit{eV}$$ , the photosensitive materials could besodium $$(\mathit{Na})$$  having work function $$\phi_o=3.75\;\mathit{eV}$$ , potassium $$(K)$$  having work function $$\phi _o=2.30\;\mathit{eV}$$  and cesium $$(\mathit{Cs})$$   having work function $$\phi _o=2.14\;\mathit{eV}$$
When using yellow-green light with incident energy, $$E_2=2.26\;\mathit{eV}$$ , the photosensitive material could be cesium $$(\mathit{Cs})$$   having work function $$\phi _o=2.14\;\mathit{eV}$$ .
When using red light with incident energy, $$E_3=1.64\;\mathit{eV}$$ , none of these photosensitive material could be used since the required condition does not satisfy.