A ray of light with wavelength is incident on three different photoelectric cells namely 1, 2 and 3. The threshold wavelength of these photoelectric cells are 1, 2, and 3, respectively and the magnitude of stopping potentials of these cells are V1, V2 and V3, respectively. The relation between and threshold wavelengths are 1 < , 2 > and 3 . The correct option is:
- V1 < V2, V3 = 0
- V1 = 0, V2 < V3
- V1 = 0, V2 > V3
- V1 > V2, V3 = 0
Answer
(2) V1 = 0, V2 < V3
Solution
Photoelectric emission occurs only when the incident wavelength is less than or equal to the threshold wavelength ( 0).
- For cell 1: 1 < , so no photoelectric emission occurs V1 = 0.
- For cells 2 and 3: 2 > and 3 > , so photoelectric effect occurs.
According to Einstein's photoelectric equation:
e Vs = hc ( 1 - 1 0 )
Since 3 2, 1 3 < 1 2, which gives:
hc ( 1 - 1 3 ) > hc ( 1 - 1 2 ) V3 > V2
Thus, V1 = 0 and V2 < V3.
Answer: (2)