A ray of light with wavelength is incident on three different photo-electric cells namely 1, 2 and 3. The threshold wavelength of these photo-electric cells are _1, _2, and _3, respectively and the magnitude of stopping potentials of these cells are V_1, V_2 and V_3, respectively. The relation between and threshold wavelengths are _1 and _3 . The correct option is :
B. V_1=0,\,V_2 < V_3
According to Einstein's photoelectric equation, the magnitude of the stopping potential V is given by: eV = hc - hc _ th For photoelectric emission to take place, the incident wavelength must be less than the threshold wavelength _ th . For cell 1, > _1. No photoelectric emission occurs, so V_1 = 0. For cell 2, 0. For cell 3, _3. Photoelectric emission occurs, and V_3 = hc e ( 1 - 1 _3 ) > 0. Since _3 and _2 > , it follows that _3 > _2, which gives 1 _3 Therefore, 1 - 1 _3 > 1 - 1 _2 , which implies V_3 > V_2. Thus, V_1 = 0 and V_2 Answer: V_1=0,\,V_2 < V_3
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