Question

The wavelengths of violet and red ends of visible spectrum are 390 nm and 760 nm respectively.

1. Evaluate the energy range of the photons of the visible light in electron volts.

2. The work function of four different materials is given in the table below.

Metal	A1	Cs	Cu	Ag
Work function (eV)	4.28	2.14	4.65	4.70

Pick out the suitable metal/ metals for the construction of the photo cell which is to operate with visible light.

3. Calculate the threshold frequency of the selected metal/metals.

Answer 1

1. 1.65 ev to 3.1 ev

2. Cs

3. hv₀ = 2.14 ev, \(\frac{2.14\times1.6\times10^{-19}}{6.6\times10^{-34}}\) = 5.187 x 10¹⁴Hz