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STD 12 - 9. Ray optics abd optical instruments — JEE STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceJEESTD 12 - 9. Ray optics abd optical instruments4 Marks
MCQ
A point source of light moves in a straight line parallel to a plane table. Consider a small portion of the table directly below the line of movement of the source. The illuminance at this portion varies with its distance $r$ from the source as
  • A
    $E \propto \frac{1}{r}$
  • B
    $E \propto \frac{1}{{{r^2}}}$
  • ✓
    $E \propto \frac{1}{{{r^3}}}$
  • D
    $E \propto \frac{1}{{{r^4}}}$
✓

Answer

Correct option: C.
$E \propto \frac{1}{{{r^3}}}$
c
(c) $I = \frac{{Lh}}{{{r^3}}}$

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