1. Tardigrade
  2. Question
  3. Physics
  4. When a monochromatic point source of light is at a distance 0.2 m from a photoelectric cell, the cut-off voltage and the saturation current are respectively, 0.6 volt and 18.0 mA. If the same source is placed 0.6 m away from the photoelectric cell, then i) VS=0.2 V ii) VS=0.6 V iii) i=6 mA iv) i=2.0 mA

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Q. When a monochromatic point source of light is at a distance $0.2\, m$ from a photoelectric cell, the cut-off voltage and the saturation current are respectively, $0.6$ volt and $18.0\, mA$. If the same source is placed $0.6 \,m$ away from the photoelectric cell, then
i) $V_{S}=0.2 V$
ii) $V_{S}=0.6 V$
iii) $i=6 mA$
iv) $i=2.0 mA$

Solution:

Stopping potential is independent of intensity
$i \propto I \Rightarrow \frac{i_{2}}{i_{1}}=\frac{I_{2}}{I_{1}}=\left(\frac{r_{1}}{r_{2}}\right)^{2} $
$\Rightarrow i_{2}=i_{1} \times\left(\frac{0.2}{0.6}\right)^{2}$
$=18 \times \frac{1}{9}=2\, m A$