The work function of a certain metal is

PHYSICS · Multi-part · CBSE · Physics · Dual Nature of Radiation and Matter · Dual Nature of Radiation and Matter

Problem

2.5\,\text{eV}

. Three monochromatic light sources S

_1

, S

_2

and S

_3

of wavelengths

450\,\text{nm}

550\,\text{nm}

and

300\,\text{nm}

, respectively, are incident normally on identical clean samples of this metal. All three beams have the same intensity. Use the constants given in Question 2. (i) For each source, calculate the stopping potential that would just reduce the photo-current to zero (state clearly if no emission takes place). (ii) Considering only those sources that do produce photo-electrons, rank them in ascending order of the stopping potential obtained. (iii) If the intensity of source S

_1

is doubled while its wavelength remains unchanged, comment qualitatively on any change, if at all, in the stopping potential calculated for S

_1

. Justify your answer briefly.

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