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11.Dual Nature of Radiation and matter
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A caesium photocell, with a steady potential difference of $60V$ across, is illuminated by a bright point source of light $50 cm$ away. When the same light is placed 1m away the photoelectrons emitted from the cell
A
Are one quarter as numerous
B
Are half as numerous
C
Each carry one quarter of their previous momentum
D
Each carry one quarter of their previous energy
Solution
(a) Number of photo electrons
$(N)$ = Intensity $ \propto \frac{1}{{{d^2}}}$
$\Rightarrow \frac{{{N_1}}}{{{N_2}}} = {\left( {\frac{{{d_2}}}{{{d_1}}}} \right)^2}$
$ \Rightarrow \frac{{{N_1}}}{{{N_2}}} = {\left( {\frac{{100}}{{50}}} \right)^2} = \frac{4}{1} $
$\Rightarrow {N_2} = \frac{{{N_1}}}{4}$.
Standard 12
Physics
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